Liquid nitrogen - storage, use and transportation within College premises 2013

Transcription

1 1. Code of Practice Liquid nitrogen - Code of Practice Liquid nitrogen - storage, use and transportation within College premises 2013

2 REVISION LOG DATE REVISION PAGE 2000 First released as guidance All 2002 Reviewed All 2003 Reviewed All 2004 Reviewed All 2012 Amended and re-launched as Code of Practice All Amendments to Responsibilities section and Transport Within Lifts section to strengthen procedural requirements with regard to this matter. 2.Changes in nomenclature to reflect re-naming of FM & Capital Projects. 3.Clarification of the 250 bar litres threshold for WSE s 4.Removal of the prohibition on lone working in Type 2 Facilities providing that lone working can be demonstrated as being under control by risk assessment. 4, 5, 15, 16, 17 and 19 Imperial College Safety Department Page 2

3 TABLE OF CONTENTS introduction... 4 Responsibilities... 4 Estates Projects... 4 Estates Facilities... 5 Academic Departments... 5 Liquid Nitrogen Service Providers... 6 Safety Department... 7 Risk assessment... 7 Properties of liquid nitrogen... 8 Hazards associated with liquid nitrogen... 8 Storage and use... 8 External storage... 8 Storage and use within laboratories and associated areas... 9 Ventilation Gas monitoring and detection Fixed monitors and alarms Portable personal monitors Transportation of cryogenic vessels Within College premises Within lifts Outside College premises Maintenance Cryogenic vessels Facilities in which liquid nitrogen is handled or stored Static installations, piped systems & Biostores Personal protective equipment (PPE) Lone working Emergency procedures Uncontrolled release of liquid nitrogen First Aid Fire Incident Reporting Information, instruction and training Disposal of cryogenic vessels Sample Storage Vessels Pressure Vessels Appendix A - Assessment of oxygen depletion Appendix B - Use of liquid nitrogen as a coolant in electron microscopes and other instrumentation Appendix C - Appendix D - Example of a planned preventative maintenance certificate for a transportable liquid nitrogen pressure vessel Example of a written scheme of examination for a transportable liquid nitrogen pressure vessel under the pressure systems safety regulations Appendix E - Treatment of cryogenic burns Appendix F - Liquid Nitrogen - Summary of requirements Imperial College Safety Department Page 3

4 INTRODUCTION INTRODUCTION 1. Compliance with the College Cryogenic Liquids Policy is mandatory and this Code of Practice (CoP) is a supporting document that must be used to assist in achieving the objectives outlined within the policy. There are sections of the CoP that will be relevant to Capital Projects, Facilities Management, Laboratory Managers, Safety Officers and anyone involved in the risk assessment process. 2. The CoP does not cover work with gaseous nitrogen or any other compressed gases. This subject is addressed in a separate Code of Practice: Safe handling, use and storage of compressed gases. The broad principles of control outlined in this CoP can be applied to other cryogenics such as liquid helium with the caveat that some properties will differ (e.g. density of the evolved gas) and some of the control measures may therefore need to be adjusted accordingly. 3. This CoP provides information on the hazards associated with liquid nitrogen and the measures to be used in controlling the risks. This information can be used to inform local procedures and risk assessments. Where relevant, references to other documents are provided in the INFOBOXES. 4. As the use of liquid nitrogen at Imperial College varies substantially from the low risk handling of very small un-pressurised quantities to the much higher large scale use of pressurised liquid nitrogen, the requirement to implement the control measures described within this CoP will also vary. So as to provide an means by which to communicate the College s requirements for the application of these control measures across the various facilities, these have been divided into 5 types (see Table 1). The College s requirements for each of these facilities is summarised within Appendix F. of this CoP. TABLE 1 LIQUID NITROGEN FACILITY TYPES Facility type TYPE 1: Biorepositories / Cryostores (supplied with Liquid Nitrogen from external static vessel via SIVL) TYPE 2: Internal areas in which pressurised vessels are used or stored Pressurised vessels are considered to be vessels operating at 0.5 bar G or more. TYPE 3: Internal areas containing nonpressurised vessels TYPE 4: Spectroscopy Facilities involving the use of liquid nitrogen TYPE 5: External storage for transportable liquid nitrogen vessels Description Discrete, dedicated facilities receiving piped liquid nitrogen supplies via a super insulated vacuum line (SIVL) from an external source either autofill or manual fill of sample vessels (or combination of both). Facilities in which pressurised liquid nitrogen vessels are used or stored. This may or may not be a dedicated room for liquid nitrogen use/storage. Facilities in which non-pressurised liquid nitrogen vessels are used or stored. This may or may not be a dedicated room for liquid nitrogen use/storage. Facilities where significant quantities of cryogens (usually liquid nitrogen and liquid helium) are employed as a coolant in association with spectrophotometers or other instrumentation. Outside facilities serving the sole purpose of accommodating transportable liquid nitrogen vessels. RESPONSIBILITIES RESPONSIBILITIES Estates Projects 5. Estates Projects have the following responsibilities: Select and employ competent contractors. Ensure that any piped liquid nitrogen system fitted as part of a capital project is installed in accordance with all relevant industry standards. For piped systems, ensure that suitable commissioning of the system is carried out and that the relevant handover documentation is provided. Information will typically include the following: Imperial College Safety Department Page 4

5 RESPONSIBILITIES Details of maximum and minimum design temperature and pressure. Details of maximum flow at design pressure. Operating instructions. Maintenance instructions. Written Scheme of Examination (WSE) Test certificates. System schematic or flow sheet. Schedule of protective devices and their function. Copy of the declaration of conformity. Ensure that the handover documentation is forwarded to Estates Facilities and user representatives and that details of any newly installed pressure systems are entered on the College insurance register. For gas sensor and alarm systems, ensure that suitable commissioning is carried out and that the relevant handover documentation is provided. Ensure that users receive appropriate training in the operation of relevant parts of the new system. Ensure that all design features of laboratories and associated areas where liquid nitrogen is to be stored, moved or used, adhere to the principles of this Code of Practice. Estates Facilities 6. Estates Facilities have the following responsibilities: Where piped liquid nitrogen systems are installed by Estates Facilities (outside the scope of a capital project), Estates Facilities shall comply with all of the responsibilities listed above under Estates Projects. Work with building occupants to ensure that liquid nitrogen can be safely transported around the premises and to designate lifts that can be used to transport liquid nitrogen between floors. Where key controlled lifts are installed, to ensure that a system is in place to enable the key(s) to be made available to liquid nitrogen users. Where it is not feasible to adapt existing lifts to enable key control, to ensure that tensa barriers are fitted within lifts as an alternative measure. Manage the contract for maintenance of oxygen depletion monitors. Coordinate, via the Customer Services Helpdesk, the arrangement of insurance inspections of piped systems and vessels at intervals defined within the WSEs. Ensure that all critical ventilation plant remains secure and is suitably maintained. Where College departments are using liquid nitrogen in NHS Trust embedded accommodation, that responsibilities for the maintenance of services, particularly ventilation, are defined and documented. With regard to the above arrangement, ensure that all critical plant is maintained in accordance with written agreements. Obtain relevant information from NHS Trust Estates (e.g. air exchange rates) and provide this information to users to enable them to utilise this information in their risk assessments. Academic Departments 7. Academic departments have the following responsibilities: Where piped liquid nitrogen systems are installed by the academic department (outside the scope of a capital project), the department shall comply with all of the responsibilities listed above under Estates Projects. Use liquid nitrogen vessels and associated systems in accordance with the operating instructions. Imperial College Safety Department Page 5

6 RESPONSIBILITIES Cooperate with Estates Facilities with regard to arrangements for insurance inspections in circumstances where such inspections are necessary. Ensure that any known defects to vessels or piped liquid nitrogen systems are reported promptly by the users to their supervisor or line manager. Ensure that no unsolicited modifications are carried out to vessels or piped liquid nitrogen systems that are likely to render them unsafe. Any modifications must be planned in consultation with cryogenics specialists. Ensure that relevant planned preventative maintenance schemes are in place for pressure vessels and piped liquid nitrogen systems. Ensure that pressure vessels are registered and logged on the College insurance register. Ensure that any gas detectors present are subject to a suitable maintenance regime. Newly installed detectors must be notified to the Customer Services Helpdesk to request that they are added to the central maintenance contract list. Ensure that any accidents or incidents involving liquid nitrogen, vessels or associated components are reported via the established College system. Provide on-the-job training to users (to include routine users checks and emergency procedures). To undertake, document and review risk assessments and SoP s associated with the storage, use and transportation of liquid nitrogen within the departments own area. To manage vessel stores / cages that belong to the department. Ensure that any new vessels and associated equipment acquired meet the required standards and are obtained from reputable suppliers. Ensure that any related equipment such as vessel trolleys, hoses and PPE are maintained in good order. Maintain operating instructions and other documentation relating to vessels, piped systems and detectors where it can be readily accessed electronically. Maintain local training records. These should also be accessible electronically. Provide assistance and advice to end users via local safety advisers. Where departments occupy embedded accommodation, to ensure that risks arising from liquid nitrogen storage and use are communicated to partner organisations in a suitable format. Where staff employed by third parties (e.g. staff of partner organisations such as NHS Trusts) use College liquid nitrogen facilities, to ensure that written agreements exist with regard to the scope of the work permitted and that the conditions of such agreements are clearly communicated to all concerned and that any such agreements are periodically reviewed to ensure that they remain current. Liquid Nitrogen Service Providers 8. Liquid nitrogen service providers shall cooperate with the College to ensure that all deliveries and movements are conducted in a safe manner. 9. Delivery drivers shall comply with any entry / exit and road traffic procedures that may be in place on College sites. 10. Delivery drivers shall report any safety related incidents to the College by the best practicable means. 11. College staff retain the right to challenge any delivery drivers deemed to be operating in an unsafe manner or to report such observations to local safety staff or the Safety Department. 12. Delivery drivers retain the right to refuse to fill any vessels if they deem it unsafe to do so. If and when such cases arise, the delivery driver shall make it clear by whatever suitable means, the reasons for not undertaking a filling procedure. In the event of safety critical faults being discovered, the delivery driver shall empty and disable the vessel and report the matter to the BOC site office at South Kensington Campus. Imperial College Safety Department Page 6

7 RESPONSIBILITIES RISK ASSESSMENT 13. Delivery drivers shall undertake pre-fill checks and annual PPM checks on all vessels provided for filling. Safety Department 14. The Safety Department has the following responsibilities: Develop College Policy and procedures for work with liquid nitrogen. Provide expert advice and support. Organise centralised training (via Learning & Development where appropriate). Liaise with the Purchasing Department with regard to any central contracts that are in for inspection and maintenance. Conduct periodic inspections and audits. Conduct periodic checks of ventilation, magnehelic gauges and gas detectors. Investigate incidents involving liquid nitrogen. RISK ASSESSMENT 15. All aspects of work involving cryogenics must be subject to the risk assessment process and this CoP assists with the practical task of completing the risk assessment. The CoP may be used in conjunction with the risk assessment template: Risk assessment for an activity involving cryogenic liquids. The process follows the familiar steps: Identify the hazards associated with the compressed gases (considering the intrinsic properties of liquid nitrogen and the general hazards arising from pressurised vessels). Identify who may be harmed and how. Decide upon suitable precautions or control measures to manage the risk. The preferred hierarchy should be to: Eliminate the need for liquid nitrogen. INFOBOX 1 Further information on bulk cryogenic liquid storage: BCGA Code of Practice 36: Bulk cryogenic liquid storage at user s premises Further information on transportable liquid nitrogen vessels: BCGA Code of Practice 27: Transportable vacuum insulated containers of not more than 1000 litres volume Copies are available in the Safety Department Prevent or minimise the risk of a liquid nitrogen release at source. TABLE 2 PRIMARY RISKS ENCOUNTERED IN THE DIFFERENT FACILITY TYPES Facility type TYPE 1: Biorepositories / Cryostores (supplied with Liquid Nitrogen from external static vessel via SIVL) TYPE 2: Internal areas in which pressurised vessels are used or stored Description Asphyxiation potential for large releases of cold gas and liquid into room. Cryogenic burns - where manual filling procedures are concerned. As for type 1 facilities plus manual handling of transportable vessels. TYPE 3: Internal areas containing non-pressurised vessels TYPE 4: Spectroscopy Facilities involving the use of liquid nitrogen TYPE 5: External storage for transportable liquid nitrogen vessels Cryogenic burns from manual filling. Low rate of boil-off and relatively small quantities of cryogen usually reduce risk of asphyxiation unless room ventilation is particularly compromised or significant spillages are possible Asphyxiation from quenching and cryogenic burns from manual transfer operations. Manual handling of vessels and cryogenic burns from spillage in transit. Imperial College Safety Department Page 7

8 RISK ASSESSMENT Disperse or dilute the resultant nitrogen gas before it reaches a critical level. Have warning systems and / or emergency procedures in place. However, as with all control measures, a combination of precautions is usually the case in practice. Document the risk assessment. Review it periodically e.g. if the work or procedures change (or immediately in the case of an adverse incident). The remainder of this CoP examines the hazards and particularly, typical control measures in some detail. The primary risks that can be encountered within the different types of liquid nitrogen storage facility are summarised in Table 2 (and also in Appendix F). STORAGE AND USE Properties of liquid nitrogen 16. Liquid nitrogen possesses the following key properties: Appearance: Colourless liquid. Nitrogen gas is invisible - the cloudy vapour which appears when liquid nitrogen is exposed to air is condensed moisture, not the gas itself. Odour: None. Boiling point: C. Density: The cold gas is heavier than air and may accumulate in confined spaces, particularly at low level. Liquid to gas expansion factor: small amounts of liquid rapidly convert to large volumes of gas - 1 litre of liquid nitrogen will generate 683 litres of gaseous nitrogen (or 0.68m 3 of gas). Hazards associated with liquid nitrogen Asphyxiation 17. One of the main dangers associated with liquid nitrogen is the risk of asphyxiation when used or stored in poorly ventilated areas. Liquid nitrogen evolves nitrogen gas which is inert and nontoxic but there is a risk of asphyxiation in situations where high concentrations may accumulate and subsequently displace air from the room. 18. Short exposures to cold gas vapour leads to discomfort in breathing whilst prolonged inhalation can produce serious affects on the lungs and could possibly provoke an asthma attack. 19. The effects of asphyxiation and methods for calculating the potential for oxygen depletion are described in Appendix 1. Cryogenic burns 20. Liquid nitrogen can cause cryogenic burns if the substance itself, or surfaces which are or have been in contact with the substance (e.g. metal transfer hoses), come into contact with the skin. Local pain may be felt as the skin cools, though intense pain can occur when cold burns thaw and, if the area affected is large enough, the person may go into shock. Frostbite 21. Continued exposure of unprotected flesh to cold atmospheres can result in frostbite. There is usually sufficient warning by local pain whilst the freezing action is taking place. Hypothermia 22. Low air temperatures arising from the proximity of liquefied gases can cause hypothermia. Susceptibility is dependent upon temperature, exposure time and the individual concerned (older people are more likely to succumb). STORAGE AND USE External storage 23. External storage commonly takes two forms: fixed static installations consisting of bulk storage tanks (often over 1000L capacity) and locations where transportable vessels (either pressurised or non-pressurised) are situated whilst awaiting refilling. 24. Static installations shall comply with the requirements of BCGA CP36. Requirements are Imperial College Safety Department Page 8

9 STORAGE AND USE EXAMPLE OF ROOM SAFETY SIGNAGE From left to right: Hazard warning (liquid nitrogen and risk of asphyxiation), access control signage (amber) with supplementary no lone working and contact information for those staff responsible for the area. The strip at the top provides instructions in relation to warning systems if present - other examples would be Do not enter if alarm is sounding and If alarm sounds leave the room immediately. described in detail in the CoP, however the salient points are as follows: Safety distances shall be in accordance with Appendix 3 of BCGA CP 36. Storage installation should be situated in the open air in a well ventilated position where there is no risk from passing vehicles. Vents, including safety relief devices shall vent to a safe place in the open so as not to impinge on personnel, occupied buildings and structural steelwork. The liquid transfer area shall be designated a No Parking area. The area must be secure so as to prevent access by unauthorised personnel. Appropriate signage shall be clearly displayed. 25. Locations where transportable vessels are held shall comply with the requirements of BCGA CP27. These requirements broadly mirror those referred to above. Storage and use within laboratories and associated areas 26. Where transportable pressurised containers and non-pressurised dewars are stored within buildings, the following points must be taken into consideration: store below 50 o C in well ventilated place. avoid storing vessels in corridors or stairwells. ensure appropriate hazard warning signs are displayed (yellow triangle with snowflake symbol and text: Liquid nitrogen ). See image above. use only properly specified equipment for storing liquid nitrogen. storage within cold rooms should not occur unless it can be demonstrated that natural evaporation and worst case scenario release would not deplete oxygen below 19.5%. Most cold rooms are well sealed and do not have any air supply or extract system, so there is little or no air change. With regard to general use: do not leave vessels unattended when filling. do not consider vessel filling to be a lone activity - always ensure others staff are on hand to raise the alarm and assist in the event of an emergency. use only transfer equipment that is designed for the purpose. do not overfill vessels. with non-pressurised containers, do not plug the entrance with any device that would interfere with the venting of gas. Use only the loose fitting necktube core or an approved accessory. do not use brittle plastics which may shatter on contact with the cold liquid. Imperial College Safety Department Page 9

10 STORAGE AND USE VENTILATION do not use hollow dipsticks - use solid metal or wood. If a warm hollow tube is inserted into liquid nitrogen, liquid will spout from the tube due to rapid expansion of liquid inside the tube and gasification. Any instructions given to staff should detail not only what they are required to do but also what they should not do. PI s have a responsibility to monitor all procedures to ensure that local rules are being complied with. VENTILATION 27. The College s standards for ventilation within the different liquid nitrogen facility types are described within line 6 of Appendix F. 28. Good ventilation is a key element of cryogenic liquid safety. If a gas release cannot be in the first place, good ventilation will help to disperse the gas and minimise the extent to which it accumulates. 29. All areas where liquid nitrogen is stored and used must be adequately ventilated, whether by natural or mechanical means. 30. No alterations to ventilation must take place without notification to FM. 31. External locations such as cages or storage areas with large expanses of louvered panels VENTILATION - SUPPLY AND EXTRACT From left to right: A door grille as a simple means of passively introducing make-up air to a room; a low level duct with side extract grill; a low level duct with bottom extract VENTILATION - ENSURING IT WORKS From left to right: A device for measuring airflow inserted into a duct; a magnehelic gauge on the wall outside a room showing the needle in the safe zone; an example of a blocked extract grille Imperial College Safety Department Page 10

11 VENTILATION GAS MONITORING AND DETECTION (particularly when arranged to permit an airflow across the area) will usually not require additional mechanical ventilation, as these can be considered to be virtually the equivalent of storage in the open air. 32. Internal locations which only benefit from natural ventilation are more problematic to assess. Factors such as the size of the room; whether it has windows or is a core room; whether it has door grilles and the quantity of liquid nitrogen stored will all need to be taken into consideration. 33. In determining what is considered to be adequate ventilation with regard to mechanically ventilated areas, 6 air changes per hour (ACH) should be taken as a minimum and this is standard for new laboratories at College. If gas detection is provided, consideration shall be given to need to link this to the ventilation so that the extract ramps up (typically to around ACH) in the event that the detector triggers (see: Gas Monitoring and Detection below). 34. All cryogenic vessels experience a natural loss of gas over time and pressurised vessels have a pressure relief valve that will temporarily lift if the pressure within the container exceeds the set value. This can be considered to be part of normal operation. For these reasons, ventilation provided within a room must be continuous so as to remove any nitrogen that may accumulate as time passes. 35. The ventilation system shall be designed so as to ensure adequate airflow around the normal operating area to prevent an asphyxiating atmosphere developing. Given that the cold gas is heavier than air, there must be low level ventilation in addition to extract at any other points within the room. Where liquid helium is also present, there must be high level extract in addition. 36. Where mechanical ventilation is required, the low level extract shall be located with the lowest part of the exhaust grille positioned no more than 10cm off the ground. Room users shall ensure that the extract points remain unobstructed. 37. Sufficient make-up air shall be provided to any room which has mechanical ventilation. 38. Air from within the room shall be extracted to a suitable external location where nitrogen cannot further accumulate. As nitrogen is a non-toxic gas, this does not necessarily need to be at roof level and may be to any well ventilated space outside the building. 39. Where mechanical ventilation is required, there shall be a means for the room users to easily determine that the ventilation is functional. This can be achieved by installing indicating devices such as warning lights or magnehelic gauges. Whilst other subjective indicators such as the sound of the ventilation system humming or the temperature within the room may provide clues to whether the extract is functioning, they are not considered an adequate sole means of determining this to be the case. 40. Access to any plant relating to ventilation systems must be adequately controlled to prevent inadvertent or malicious tampering and all controls shall be identified with suitable signage indicating clearly the on and off positions and warning that the equipment is critical to safety. 41. All ventilation systems shall be subject to suitable maintenance regimes as described within line 18 of Appendix F. GAS MONITORING AND DETECTION Fixed monitors and alarms 42. Prevention of an uncontrolled release is the first priority in the gas control hierarchy followed by the availability of good ventilation to disperse the gas in the event that the release cannot be prevented. Only when these points have received attention should the issue of gas monitoring and detection be considered. There is often a temptation to readily install gas monitors and detectors without due consideration of what is involved. There can certainly be drawbacks: initial installation can be expensive. ongoing maintenance can be expensive. they can fall into neglect. neglect and lack of maintenance can cause faults to develop. As a result, they may not function when they need to and may also develop nuisance triggering when no oxygen depletion is taking place. if users have little understanding of why they are present or little confidence that they Imperial College Safety Department Page 11

12 GAS MONITORING AND DETECTION GAS DETECTORS AND ALARMS From left to right: A detector incorporating a digital display showing oxygen concentration; a two stage detector / alarm with flashing lights at low and critically low O2; a high-spec control panel WARNING SYSTEMS From left to right: Three different designs of visual warning beacons incorporating audible sounders located outside liquid nitrogen rooms SENSORS AND PORTABLE ALARMS From left to right: Two examples of different designed oxygen sensor housings and a typical portable low oxygen monitor with digital readout and flashing alarm Imperial College Safety Department Page 12

13 GAS MONITORING AND DETECTION function correctly, they will be ignored. Their presence is therefore rendered useless. 43. To determine whether oxygen depletion monitoring is necessary, the following guidelines must be applied (note that the College s requirements for detectors and alarms are described in line 8 of Appendix F): Monitoring must be in place in all instances where liquid nitrogen is piped from an external static storage vessel to the point of use. In such situations, there is clearly the potential for large quantities of liquid or gas to be discharged into the room in the event of something going wrong. Also, under normal operating conditions where dispensing takes place manually, it is not uncommon for several minutes to pass before liquid appears at the discharge point. Prior to that point, gaseous nitrogen is being deliberately discharged into the room. With regard to pressure vessels, monitoring must be in place where an uncontrolled release from the largest vessel present within the area would give rise to an oxygen deficient atmosphere of below 18% (the worst case scenario calculation). With regard to non-pressurised vessels, monitoring must be in place where the maximum foreseeable spillage would give rise to an oxygen deficient atmosphere of below 18%. This is most relevant where manual tipping operations are carried out from the likes of onion dewars and dropping the dewar is a foreseeable risk. Free standing sample fridges are very unlikely to topple over. Monitoring must be in place where the natural evaporation from rate from non-pressurised vessels may give rise to an oxygen deficient atmosphere of below 18% (the cumulative rate if several are present). However, this is very unlikely in practice unless there are a large number of vessels in a vey small room with poor ventilation - in which case, the first option must be to find a more suitable location. 44. If the risk assessment determines that monitoring is necessary, then there are a number of points that must be addressed: The detector must be of the correct type, fitted with an oxygen sensor(s). It should be purchased and installed via Estates Facilities to ensure that the contractors are able to recommend a College approved make. The sensor(s) must be positioned where they will readily detect a nitrogen release i.e. - in proximity to the potential source of release but not close enough to cause continual nuisance triggering. - at a height recommended by the manufacturer but typically no more than 1m above floor level i.e. below the breathing zone of the average person. Where liquid helium is also present, there will need to be detection at high level in addition. - Above the location of any low level extract grilles. This will drastically reduce the likelihood of nuisance triggering. - unobstructed by equipment or other items (including temporarily located items). - in a position where they can be accessed for maintenance without too much difficulty. The detector must be suitably calibrated and the set-points programmed at a level appropriate to detecting oxygen depletion. The normal set-point for a low oxygen alarm is 18% oxygen. Where a two stage alarm is fitted, the first stage alarm should be set at 19.5% and the second stage alarm at 18%. Periodic testing of alarms will be carried out by the Safety Department using a suitable test gas and the results of the test recorded. This will be part of a rolling programme and carried out in conjunction with ventilation and magnehelic checking. Alarms audible and / or visual must be of the fixed type and must be present both within the laboratory (so that occupants can leave) and also outside the laboratory (so that others do not enter). This requirement dictates that detectors will normally need to be mains powered rather than battery powered unless there is a means of installing battery powered Imperial College Safety Department Page 13

14 GAS MONITORING AND DETECTION TRANSPORT OF VESSELS detectors in a way that satisfies this requirement. Alarms must be assessed to determine whether any additional functionality is required e.g. whether the alarm needs to be linked to a solenoid valve that automatically shuts of the gas supply when it is triggered. Alternatively, alarms can be linked to mechanical ventilation to enable the extract to be ramped up in the event of it triggering. These features are usual for piped installations. Alarm panels are best located outside the area of the potential gas release. If necessary, they can then be interrogated from a position of relative safety.. system must be subject to a maintenance regime. Some sensors require replacement or recalibration as frequently as every six months. All users of the area must receive local training so that they are aware of what the alarms mean and what to do in the event of them sounding. This information should be recorded in local protocols. Portable personal monitors 45. Portable personal monitors may be considered in addition to, but not as an alternative to, fixed detection systems. The following points should be borne in mind: They may also require maintenance to keep them functioning (though fixed lifetime no maintenance models may be available). They will only provide a warning if the user remembers to wear it. They will only provide an appropriate level of warning once the gas enters the vicinity of the monitor (rather than at the source of the leak if this happens some distance away). TRANSPORTATION OF CRYOGENIC VESSELS Within College premises 46. If vessels must be manoeuvred between locations and there is a risk or possible risk of injury then an assessment must be carried out under the Manual Handling Operations Regulations. This should be carried out by the users with advice and assistance from the local Manual Handling Assessor or other suitably qualified individual. 47. Pressurised vessels and non-pressurised dewars are extensively used throughout the College - a full 250 litre pressurised vessel can weigh up to 400 kg and manual handling injuries can, and have been sustained by College staff. Further advice and a manual handling checklist is available on the Occupational Health web page ( guidanceandadvice/manualhandling). In the case of the larger pressurised cylinders, it is highly likely that the assessment will indicate that the movement of these vessels should be a two person operation, particularly if there is a requirement to move between differing levels using a lift (see below). Before moving transportable containers, the route should be assessed to consider: rest stops movement through populated work areas possible obstructions and clutter lifts (see below) floor surfaces (are they sound and even?) kerbs, pavements and road surfaces (damaged surfaces should be reported via the FM Helpdesk. Beware of traffic movements. stairs (hazardous due to potential for slips and trips which could result in spillages from small hand held dewars) whether the destination for the vessel is ready to accept it 48. Only purpose designed handling equipment should be used. A wide range of trolleys are commercially available for transportation of both pressurised and non-pressurised tanks, including roller base-tipping trolleys for the latter, which enable both transportation and safe pouring (but only if the receiving vessel is at an appropriate height). Other accessories are also available such as withdrawal devices which can be fitted to non-pressurised dewars to facilitate Imperial College Safety Department Page 14

15 TRANSPORT OF VESSELS withdrawal without the need for tipping and pouring. Within lifts 49. Vessels must only be transported in lifts when covered by a safe system of work which takes account of the hazards, including that due to oxygen deficiency when a lift is stopped for a period between floors (Transportable Vacuum Insulated Containers of not more than 1000 Litres Volume - BCGA Code of Practice CP27). 50. In practice, this means that pressurised vessels (and dewars) must not be accompanied in lifts - measures must be taken to close the lift to all passengers. The vessel should be manoeuvred into the lift and the lift sent to it s destination floor to be met by an assistant. It must not be a one-person operation that involves this person hurrying up or down the stairs to meet the vessel at its destination floor. A system should be employed to ensure that no passenger enters the lift at intermediate floors. If the lift has a key mechanism which permits the operator to take control then this is the preferred option, though in reality this may not be possible due to the lift design. If this is the case, then a barrier (chain / tensa etc.) together with an appropriate warning sign ( Do not enter - liquid nitrogen in transit ) must be deployed within the lift to prevent persons entering. A sign alone is not sufficient in the absence of a physical barrier. 51. Goods lifts must be used in preference to passenger lifts. Where a goods lift does not exist, a passenger lift may be used as an alternative as long as this is agreed by Estates Facilities and is equipped in the same way as a goods lift - either with key control or fitted with a tensa barrier. 52. If, for any reason the floor of the lift does not finish flush with the floor outside the lift (i.e. there is a small step up or down), then this should be reported immediately so that the lift engineers can work to correct the fault. Under these circumstances extra care should be observed whilst manoeuvring the vessel in and out - one person should be charged with ensuring that the lift doors are held open during this process. 53. BCGA and BOC advise that when the use of lifts cannot be avoided, one or more of the following shall be adopted: The vessel should be vented until the pressure falls below 60% of the relief valve setpressure (in a safe place). Otherwise, non-pressurised dewars shall only be filled to 90% of net capacity. The operator should be equipped with an oxygen monitor and have control of the lift. There should be additional personnel outside who are aware of the operation. The lift should be equipped with an emergency alarm / telephone. However, there are some dangers associated with the above points: Venting the vessel may be a risky procedure in itself and, at best, it will only buy the operator additional time before the oxygen atmosphere within the lift depletes should it become stuck between floors. The possession of an oxygen monitor will warn the occupant of oxygen depletion (arguably increasing the likelihood of panic) but will not assist escape in any way. A rapid response will be required if the alarm is raised. It is therefore established College procedure that all vessels shall travel unaccompanied. The only exemption is very small quantities of liquid nitrogen contained in suitable hand-held vessels (see Para 55). 54. Vessels shall not be transported in lifts if they are: Leaking or obviously defective. Venting gas. Overfilled. INFOBOX 2 Further information on Pressure Systems Regulations: BCGA Code of Practice 23: Application of the Pressure Systems Safety Regulations to Industrial and Medical Pressure Systems Installed at User Premises Further information on static liquid nitrogen vessels: BCGA Code of Practice 28: Vacuum Insulated Tanks of not more than 1000 litres Volume which are Static Installations at User Premises Copies are available in the Safety Department. Imperial College Safety Department Page 15

16 TRANSPORT OF VESSELS Coated in ice on the outside (this may indicate deterioration in the vacuum). 55. Small volumes of liquid nitrogen in hand held dewars may be accompanied in goods lifts providing the assessment reveals that evaporation or spillage of the complete contents would not significantly reduce the oxygen level within the lift. This must be determined by calculation (see Appendix 1). Outside College premises 56. The transportation of cryogenic vessels off site is not a mainstream activity for College staff. If cryogenic vessels are to be transported off site, this must be carried out in compliance with all PRESSURE VESSEL LABELLING Left: College registration label showing unique reference number and QR code. From left to right: Two examples of planned preventative maintenance (PPM) labels attached to transportable pressure vessels; a disc indicating the replacement date for a pressure relief valve (June 2013) FEATURES OF LIQUID NITROGEN FACILITIES From left to right: An emergency E-Stop button for manually isolating piped liquid supply; a dead man s pedal for dispensing liquid nitrogen from a piped supply (sitting on an epoxy floor); a vinyl floor showing signs of excessive damage consistent with liquid nitrogen contact Imperial College Safety Department Page 16

17 MAINTENANCE regulations relating to the transport of dangerous goods. These regulations are complex and your local safety adviser or the Safety Department must be consulted in all cases. MAINTENANCE Cryogenic vessels 57. All static and transportable pressurised vessels must be subject to a Planned Preventative Maintenance scheme. An example of a PPM certificate is given in Appendix C. 58. Pressure vessels having a pressure / volume product exceeding 250 bar litres must also be examined in accordance with a Written Scheme of Examination (WSE) under the Pressure Systems Safety Regulations. Completion of a written scheme of examination and the periodic examination itself is usually carried out by a trained engineer appointed by the College insurers. Alternatively, if the vessel is rented, this may be arranged by the owners of the vessel. Pressure vessels may be registered with the Customer Services Helpdesk by completing and submitted the relevant form available on the Safety Department website: safety/subjects/pressuresystems. Though details of the examination are primarily the concern of the insurance inspector, guidelines pertaining to Written Schemes of Examination (WSE) for cryogenic liquid storage systems are given in Appendix 2 of BCGA CP23. An example of a WSE for a transportable pressure vessel is given in Appendix D. 59. Non-pressurised vessels should be subject to routine visual examination by the users to ensure that they are damage free and fit for purpose. 60. Trolleys and wheels, though not always an integral part of the vessel, must also be subject to visual examination and repair where necessary. Damaged parts must be reported and repaired or replaced. 61. for ensuring that cryogenic vessels are suitably examined and maintained rests with the Department or Section that owns the vessel. 62. All transportable pressure vessels must bear the following labels / markings: Dataplate (engraved). Valve labels (metal disks indicating the functions of the valves. Decommissioning tag (metal disk stating the date of decommission). The decommission tag does not necessarily indicate the end of the lifetime of the vessel, but it must not be used beyond this date without repair or replacement of the relief valve (example above). Product label (hazard label /transport information). PPM label (often a sticky label indicating the maintenance and inspection history) (examples above). Vessel ID tag (usually a laminated tag with BOC account number identifying the owner). A College registration label that identifies the vessel on a central database (example above). 63. All records of examination and maintenance must held by the Department or Section in a format accessible to present to the enforcing authorities if requested. 64. Any obvious damage sustained by vessels (either static or transportable) must be reported immediately to the Laboratory Supervisor and if necessary, the vessel should be taken out of use until inspected by a competent person. STATIC INSTALLATIONS, PIPED SYSTEMS AND BIOSTORES Facilities in which liquid nitrogen is handled or stored 65. The different requirements for maintenance and performance validation of facilities in which liquid nitrogen is handled or stored are described in line 18 of Appendix F. STATIC INSTALLATIONS, PIPED SYSTEMS & BIOSTORES 66. The design and installation of such facilities should be in accordance with BCGA Code of Practice CP21 and BCGA Code of Practice CP28. In addition to these Codes of Practice, the following design features relate to laboratories which receive piped supplies: Manually operated emergency stop buttons must be included. These will be used to isolate the liquid nitrogen flow via a solenoid valve in the event of an emergency. These must be located within the room close to the exit door and external to the room just outside the door, thus enabling users to quickly get clear of the danger zone and safely Imperial College Safety Department Page 17

18 STATIC INSTALLATIONS, PIPED SYSTEMS AND BIOSTORES PERSONAL PROTECTIVE EQUIPMENT isolate the flow in the event of an abnormal situation arising. This also permits third parties to stem the nitrogen flow without needing to enter the danger zone should they notice a problem e.g. an unconscious casualty within the room. Despite all precautions, drips and small spillages are likely to occur. Vinyl flooring will eventually crack and lift, presenting both a contamination and a trip hazard. The area (or at least the area immediately beneath the tap) must therefore be fitted with a suitably resistant flooring material - epoxy resin, aluminium, stainless steel or high density polyethylene (HDPE). Judgement will need to be used regarding the extent of the area to be covered though it should be borne in mind that even a small spillage will spread a considerable distance. Epoxy flooring provides a highly resistant, easily cleanable and aesthetically pleasing surface for whole room coverage. Vessels shall be arranged in a manner that permits good accessibility and movement around them. Manual filling points (if present) shall be located away from doors and in a position where the users can easily retreat to safety in the event of a problem developing. Devices such as dead man s handles (or pedals) can be considered for manual filling points. This will ensure that the hose will only deliver liquid nitrogen when an operator the lever or button (or pedal) and will cut the supply in the event of the lever, button or pedal being released. Sections of laboratory benching should be provided for sample sorting. Doors must be fitted with vision panels that permit viewing of all parts of the room. Mirrors may be employed to aid viewing of areas that are not within the direct sight line of the vision panels. Vision panels must remain unobstructed. Door thresholds must be free of ridges to permit easy movement of transportable vessels in and out of the facility. If the size and configuration of the room is such that escape in the event of an emergency could be difficult, an additional door(s) to the facility must be provided. CCTV cameras or webcams should be considered. Where cameras are installed, consideration must also be given as to who will monitor them. A suitable location for storage of PPE must be provided. PERSONAL PROTECTIVE EQUIPMENT (PPE) This must be appropriate to the task in hand and readily available. 67. Hands - non-absorbent insulated gloves must always be worn when handling anything that is or has been in recent contact with liquid nitrogen. Cryogenic gloves are designed to be used in the vapour phase only and should not be immersed into liquid nitrogen under any circumstances. If gauntlet style gloves are chosen, lab coat sleeves should cover the ends of gloves to ensure that liquid cannot get between the glove and the hand or the gauntlet must be tight enough around the forearm so as to prevent any liquid from entering. Alternatively, a ribbed cuff style may be used. There are a range of commercially available gloves suitable for use at cold temperatures - gloves that are used with liquid nitrogen should meet the requirements of BS EN 155: 2006 Protective gloves against cold. 68. Face - a full face visor should be used to protect the eyes and face where splashing or spraying may occur and, in particular, where operations are carried out at eye level e.g. when topping up reservoirs on electron microscopes Body - a laboratory coat or overalls should be worn at all times. Non-absorbent cryogenic aprons are also commercially available. Open pockets and turn-ups where liquid could collect should be avoided. Trouser bottoms should overlap boots or shoes for the same reason. 70. Feet - sturdy shoes are recommended for handling liquid nitrogen vessels. Open toed shoes must not be worn under any circumstances. 71. When not in use, all PPE should be stored in an appropriate manner (e.g. visors on wall mounted hooks) to ensure that it does not become damaged or contaminated. Imperial College Safety Department Page 18

19 LONE WORKING EMERGENCY PROCEDURES LONE WORKING 72. The department must have established lone working procedures and these must be applied to work with liquid nitrogen. Due consideration must be given to the fact that the consequences of an incident involving liquid nitrogen whilst lone working can be catastrophic. 73. Lone working with significant quantities of liquid nitrogen must be avoided. Measures must be in place to ensure that assistance is always at hand by employing buddy systems, CCTV, mandown alarms etc where appropriate. Lone working in Type 2 facilities can present significant risks, especially in small rooms and is prohibited unless it can be demonstrated by risk assessment that it is safe to do so. Lone working with liquid nitrogen in Type 1 facilities is prohibited. EMERGENCY PROCEDURES 74. The following emergency procedures are generic responses. Emergency procedures must be in the risk assessment and communicated to all involved, including others who may be part of the response process or first on the scene e.g. Security. For areas designated as amber or red under the College Access Control scheme, procedures must be documented in an Emergency Response Plan in a standard format. Uncontrolled release of liquid nitrogen If no casualties are present 75. Evacuate the area. Deploy warning signs if necessary. 76. Ventilate the area. Open doors and windows or activate forced ventilation if safe to do so, to allow any spilt liquid to evaporate and the resultant gas to disperse. 77. Try to stop the release if at all possible e.g. activate emergency stops or turn off valves, but only if it is safe to do so. 78. Prevent liquid nitrogen from entering drains, basements, pits or any confined space where accumulation may be dangerous 79. Do not re-enter area without self-contained breathing apparatus (BA) unless it is proved safe to do so (see below with regard to use of BA). The presence of oxygen deficiency monitors will indicate the oxygen levels in the vicinity. 80. Liquid nitrogen is used in many locations throughout the College. In most cases, it is not practicable to have breathing apparatus available. There are a number of reasons for this: - The cost of purchasing the apparatus. - The cost of maintaining the apparatus. A good maintenance regime is essential. - BA must only be used by trained personnel. Training must be kept up-to-date. - The need to select individuals who are medically fit to wear BA. 81. The emphasis must therefore focus upon not entering the room until the atmosphere is known to have returned to normal. The extent and location of the release will determine whether it is necessary to evacuate only the immediate area or to evacuate a wider area such as the whole building. This will need to be decided on a case -by-case basis and judgement will be required. 82. If an alarm is found to be sounding, it must be assumed that there is potentially an oxygen deficient atmosphere present. Do not automatically assume that there has been a sensor failure and enter the room without taking any precautions. If casualties are present 83. If no alarm is sounding or if there is no visual evidence that the casualty has been overcome by an oxygen deficient atmosphere, enter with caution and treat as a medical emergency. 84. If alarms are sounding or there is evidence of a liquid nitrogen release, do not enter the room. In the event of an unconscious casualty, the emergency services must be summoned both medical and the Fire Brigade (who will be equipped with BA). In such a situation, time will be crucial and there will quite likely, not be enough time. It is therefore important that all the proactive measures described in this CoP are taken so as to reduce the likelihood of an unconscious casualty to a negligible level. 85. Follow the same advice in paras above. Imperial College Safety Department Page 19

20 EMERGENCY PROCEDURES First Aid 86. Where inhalation has occurred, the victim (who may be unconscious) should be removed to a well ventilated area. Rescuers must not put themselves at risk - a contaminated area should not be entered unless considered safe. Breathing apparatus may be required but should only be used by trained personnel. The person should be kept warm and rested whilst medical attention is obtained. If breathing has stopped then resuscitation should be commenced by a trained first aider. 87. Where contact has occurred, the aim should be to slowly raise the temperature of the affected area back to normal. For minor injuries, clothing should be loosened and the person made comfortable. Clothing should not be pulled away from burned or frozen skin. The affected area should be doused with copious quantities of tepid water (40 o C) for at least 15 minutes and a sterile burn dressing applied to protect the injury until the person can be taken to receive hospital treatment. Do not: use a direct source of heat such as a radiator. permit smoking or alcohol consumption. give analgesics (e.g. paracetamol, aspirin). For major injuries apply first aid as far as is practicable and arrange for the victim to receive medical attention. On arrival at hospital, medical staff should be provided with a copy of BOC Gases Guidance Note G4968 Treatment by medical practitioner or hospital (see Appendix E). INFORMATION, INSTRUCTION & TRAINING Fire 88. Nitrogen is a non-flammable gas but any vessels under pressure may explode when exposed to fire, irrespective of the type of gas contained within. There are certain general actions that should be taken: Operate the planned fire drill for the area in question. College staff should not attempt to fight fires involving (or near) vessels unless it is small enough to be dealt with very quickly activate the fire alarm call point and get out of the building. Where piped systems are concerned, if possible, isolate the liquid nitrogen supply to the area affected but do not take any risks. Keep emergency response team appraised of any actions taken with regard to isolations - either successful or unsuccessful. As with any fire, do not re-enter the building until clearance has been given. Vessels that have been heated can remain dangerous even after the fire has been extinguished. Incident Reporting 89. Any incident involving liquid nitrogen, vessels or associated pipework (irrespective of whether any injury or exposure occurred) must be reported via the established College system. Examples include: dropped or toppled vessels significant release of liquid or gas either from direct spillage or failed components. visibly damaged components including hoses, wheels and trolley parts. INFORMATION, INSTRUCTION AND TRAINING 90. All users of compressed gases must receive adequate information, instruction and training. This takes several forms: Provision of information. Users must be able to access Material Safety Data Sheets and assessments / SOPs for the activity. They must understand the hazards associated with the gases they are using and the controls necessary to maintain safety. Better still, they should be actively involved in the risk assessment process from the outset. Formal training. The College offers a number of formal training courses on the use of compressed gases. This includes an E-Learning course: Using Liquid Nitrogen Safely within Universities and a practical course on decanting liquid nitrogen. details of courses may be found on the Learning and Development website: Imperial College Safety Department Page 20

21 INFORMATION, INSTRUCTION & TRAINING DISPOSAL OF VESSELS www3.imperial.ac.uk/staffdevelopment/safety On-the-job training. This includes practical instruction (and if necessary adequate supervision) on the use of specific apparatus in the area where the individual is expected to work. This must include instruction on routine observation of controls such as alarms, indicators that ventilation is working, local lone working procedures and emergency procedures. DISPOSAL OF CRYOGENIC VESSELS Sample Storage Vessels 91. Ensure that the vessel is empty of liquid nitrogen (transfer and / or allow to convert to gas naturally in a well ventilated area). 92. Remove sample racks and samples. Check for loose specimen tubes (particularly under baseplate) and remove for appropriate disposal. 93. Thoroughly clean all accessible surfaces (including racks) with suitably validated disinfectant. 94. Append decontamination certificate and dispose via an appropriate route e.g. as equipment waste via Estates Facilities. 95. Ensure that details of any disposed vessels are removed from inspection registers. Pressure Vessels 96. Empty vessel by transferring liquid. Once bulk of liquid has been removed, open relevant valve to enable remainder of gas to escape in a safe, well ventilated area e.g. outdoors. 97. Append a decontamination certificate and dispose via an appropriate route. There should be no particular measures to take with regard to decontamination, though the certificate will still be required and this fact can be recorded on the certificate. Imperial College Safety Department Page 21

22 APPENDIX A - ASSESSMENT OF OXYGEN DEPLETION 1. Nitrogen is the main component of air and is present at approximately 78% by volume (oxygen is approximately 21% and argon 1%). Any alterations in the concentrations of these gases, especially oxygen, have an effect on life. In the case of liquid nitrogen, there is a risk of asphyxiation where ventilation is inadequate and the nitrogen gas evolved can build up and displace oxygen from the local atmosphere. An atmosphere containing less than 18% oxygen is potentially hazardous and entry into atmospheres containing less than 20% should be avoided. 2. The general effects of reduced oxygen content in the atmosphere are given in the table below. However, it should be recognised that the response to oxygen deficient atmospheres can vary significantly between individuals. Sudden asphyxiation, such as inhalation of pure nitrogen, is likely to cause instant unconsciousness. Even in the case of gradual asphyxia due to a gradual reduction of the oxygen in the atmosphere, the victim may have little warning. 3. There are three common scenarios for which calculations can be performed to ascertain oxygen depletion levels. It should however, be recognised that this is not an exact science and circumstances may dictate that the actual situation may vary due to factors such as stratification i.e. where nitrogen may accumulate at low level and distribution may not be uniform throughout a room. Oxygen content (% volume) Standards, effects and symptoms ~ < Two breaths of pure nitrogen Normal oxygen concentration in air Minimum oxygen concentration at which the workplace should be maintained Potentially dangerous atmosphere - entry into room should be prohibited Physical and intellectual performance diminishes without the person being aware Possibility of fainting without prior warning Fainting within a few minutes - resuscitation possible if carried out immediately Fainting almost immediate, death ensues, brain damage even if resuscitated Immediate loss of consciousness and death within two minutes Example 1: Natural evaporation scenario - amount of gas evolved from vessels in their normal state In typical situations the concentration of nitrogen gas that may accumulate in a room over a period of time (assuming a certain evaporation rate from vessels and / or pipework) may be calculated using the following equation: C = L / Vn (approximately) Where: C = gas concentration L = gas release (m 3 / h) V = room volume (m 3 ) n = air changes per hour For rooms at or above ground level, natural ventilation will typically provide 1 air change per hour. However, this is not the case with rooms which are windowless or have windows which are tightly sealed, in which case the number of air changes will be less than 1 per hour. For underground rooms with small windows, 0.4 changes per hour could be considered a typical value. L = (6 x 0.5) x 2 x 683 / (24 x 1000) = m 3 / h V = 33.6 m 3 n = 0.5 therefore: C = / (33.6 x 0.5) = (x 100) = 1.0% The nitrogen concentration of the room is increased by 1.0%. The normal oxygen content of the atmosphere is approximately 21%, therefore: 21 x (100 / ( )) = 20.8% Oxygen Imperial College Safety Department Page 22

23 Room volume (H=2.8m, W=3.0m, D=4m) [m3] 33.6 Number of non-pressurised liquid nitrogen vessels stored in room 6 Capacity of each vessel [litres] 25 Natural rate of evaporation (obtainable from the manufacturers specification -typically 1 or 2% of the liquid capacity in a 24 hour period [litres] 0.5 Factor to be multiplied to account for deterioration in the vacuum insulation over time 2 Estimated air changes per hour by natural ventilation 0.5 Gas expansion factor for liquid nitrogen 683 Under these circumstances the evaporation from the vessels only reduces the atmospheric oxygen content from 21% to 20.8% - negligible and well within the safe working limit. Example 2: Losses associated with filling operations During filling operations, when the lids of the vessels are open and liquid nitrogen is being transferred, there will be an increase in the amount of gas generated. In most cases, this is a relatively short term operation and the increase may not be significant, as the following example demonstrates. Each vessel is topped-up one at a time every three days. We have already estimated that the vessel loses 1.0 L by evaporation in 24 hours (0.5 L doubled to account for deterioration in vacuum). Therefore, 3.0 L will be lost in 72 hours and will need to be replaced. We can assume that 10% (0.3 L) of this will go to atmosphere during the topping-up process: 0.3 x 683 = 205 L = m / 33.6 (room volume) = 0.6% nitrogen added to atmosphere 21 x (100 / ( )) = 20.8% The oxygen in the atmosphere during the topping up process is reduced no further. Example 3: Worst case scenario - instant and uniform release of the entire contents of a vessel Alternatively, oxygen deficiency resulting from a large spillage of liquid nitrogen or sudden rapid release of nitrogen gas from a pressurised vessel may be calculated as follows - this is the worst case scenario : Resulting oxygen concentration (%) %O2 = 100 x (Vo / Vr) Where, for nitrogen: Vo = (Vr - Vg) Vr = room volume (m 3 ) Vg = maximum gas release, which is the liquid volume capacity of the vessel V x gas expansion factor. A pressurised liquid nitrogen vessel of 100 litre capacity located in a room 2.8 m x 5.0m x 10.0m loses vacuum suddenly and vents it s contents to atmosphere in a very short space of time: Vr = 2.8 x 5.0 x 10.0 = 140 m 3 Vg = 100 x 683 = litres = 68.3m 3 Vo = ( ) = %O2 = 100 x (15.02 / 140) = 10.7% The oxygen content of the room is halved to 10.7%. Imperial College Safety Department Page 23

24 APPENDIX B - USE OF LIQUID NITROGEN AS A COOLANT IN ELECTRON MICROSCOPES AND OTHER INSTRUMENTATION 1. Electron microscopes and other instruments such as NMR spectrometers require liquid nitrogen as a coolant and are present in a number of departments throughout the College. It is the accepted practice to fill reservoirs by attaching a hose from a pressure vessel or pouring liquid nitrogen directly from a small hand held dewar. Some reservoirs are over 2m from floor level. When transferring liquid nitrogen at such a height, special care is needed and the following precautions should be taken: platform steps with a guard rail should be considered. They should be of sufficient height to enable the reservoir to be filled from above rather than at face level. A number of factors affect the practicality of using ladders, such as the ceiling height and the amount of space available for manoeuvring them into place. Care must be taken not to introduce additional risks such as tripping over or pulling loose electrical cables. If there is sufficient space to leave the ladder permanently in place behind the instrument then this should be considered. if the height of the ceiling is restrictive and filling must subsequently take place close to face level then it is essential to wear a full face visor. Since there is also a greater risk of liquid nitrogen being spilt down the person s front, then suitable clothing which minimises neck and chest exposure and the likelihood of liquid nitrogen being trapped against the skin should be chosen e.g. a pocketless laboratory coat buttoned up so that it comes above the bottom rim of the visor and / or a cryogenic apron. Where hoses are used to transfer liquid nitrogen from pressure vessels, the hoses must be attached securely to the fill nozzle and be constructed from a material that is resistant to liquid nitrogen. while the task is being performed, at least one other person should be present in the vicinity to raise the alarm and assist in the event of a mishap. The second person however, should never stand immediately beneath the person who is filling since they may become a victim themselves if there is a spillage or the flask is dropped. the person filling should remain vigilant so that any overflow from the reservoir is strictly limited and does not splash in the vicinity of passing people. If a hose is attached to the overflow, it should be positioned in a way that does not present a risk to personnel. the hand held dewar should be approved for use with cryogenic substances. MAGNET BEING FILLED FROM A PRESSURE VESSEL The operator stands a safe distance from the exhaust hose and is ready to turn off the feed at the point where liquid appears. Mats have been laid to protect the floor from liquid nitrogen overspill. The operator also has a clear view in the event that anyone else approaches during the operation. Imperial College Safety Department Page 24

25 APPENDIX C - EXAMPLE OF A PLANNED PREVENTATIVE MAINTENANCE CERTIFICATE FOR A TRANSPORTABLE LIQUID NITROGEN PRESSURE VESSEL Imperial College Safety Department Page 25

26 APPENDIX D - EXAMPLE OF A WRITTEN SCHEME OF EXAMINATION FOR A TRANSPORTABLE LIQUID NITROGEN PRESSURE VESSEL UNDER THE PRESSURE SYSTEMS SAFETY REGULATIONS Imperial College Safety Department Page 26

27 APPENDIX E - TREATMENT OF CRYOGENIC BURNS Imperial College Safety Department Page 27

28 LIQUID NITROGEN ISSUE 2012 APPENDIX F - LIQUID NITROGEN - SUMMARY OF REQUIREMENTS Code of Practice Liquid nitrogen - summary of requirements The following table provides a summary of the requirements that must be met for the different types of facilities in which liquid cryogenics are stored or handled at Imperial College. These requirements are as those described within the College Code of Practice Storage, use and transportation of liquid nitrogen in College premises and as such are implemented with the College s Safety Management System by the Cryogenic Liquid Safety Policy. TYPE 1 Biorepositories / Cryostores (supplied with LiqN from external static vessel via SIVL) TYPE 2 Internal areas in which pressurised vessels are used or stored TYPE 3 Internal areas containing nonpressurised vessels TYPE 4 Spectroscopy Facilities involving the use of LiqN TYPE 5 External storage for transportable LiqN vessels 1 Description Discrete, dedicated facilities receiving piped LiqN supplies via a SIVL from an external source either autofill or manual fill of sample vessels (or combination of both). Facilities in which pressurised LiqN vessels are used or stored. This may or may not be a dedicated room for LiqN use/storage. Facilities in which nonpressurised LiqN vessels are used or stored. This may or may not be a dedicated room for LiqN use/storage. Facilities where significant quantities of cryogens (usually LiqN and liquid helium) are employed as a coolant in association with spectrophotom eters or other instrumentation. Outside facilities serving the sole purpose of accommodating transportable LiqN vessels. 2 Primary risk(s) Asphyxiation potential for large releasess of cold gas and liquid into room. Cryogenic burns - where manual filling procedures are concerned. As for type 1 facilities plus manual handling of transportable vessels. Cryogenic burns from manual filling. Low rate of boiloff and relatively small quantities of cryogen usually reduce risk of asphyxiation unless room ventilation is particularly compromised or significant spillages are possible Asphyxiation from quenching and cryogenic burns from manual transfer operations. Manual handling of vessels and cryogenic burns from spillage in transit. Imperial College Safety Department Page 28

29 LIQUID NITROGEN ISSUE 2012 TYPE 1 Biorepositories / Cryostores (supplied with LiqN from external static vessel via SIVL) TYPE 2 Internal areas in which pressurised vessels are used or stored TYPE 3 Internal areas containing nonpressurised vessels TYPE 4 Spectroscopy Facilities involving the use of LiqN TYPE 5 External storage for transportable LiqN vessels 3 Location of Facility Should be located so as to minimise the length of SIVL pipelines and with due consideration to the installation of large vessels. Consideration must be given to the requirement to move transportable vessels to and from the location. The need to move vessels in lifts should be minimised. Where the area is of mixed use then the risk assessment must also take account of the risks to others not directly using the LiqN. Sufficient space must be available to adequately segregate non-users from those handling the cryogen. Storage and filling points should be located in a part of the lab away from other activities and traffic routes. Consideration must be given to the requirement to move transportable vessels to and from the location. The need to move vessels in lifts should be minimised. Storage and filling points should be located in a part of the lab away from other activities and traffic routes. Consideration must be given to the requirement to move transportable vessels to and from the location. The need to move vessels in lifts should be minimised. Magnets should be segregated from other activities. Requires good vehicle access for deliveries. Due consideration must be given to route that vessels take into the building. 4 Security Electronic access control system required Physical access controls most commonly swipe card or to room. proximity card must be present for internal locations. Individual room access control is preferred if the configuration permits this arrangement, particularly if the room is accessed via a general corridor or a mixed use area. Access control to the floor or area is permissible if the configuration does not lend itself to individual room security. A secure lockable cage or enclosure should be provided. Padlocks and chains on vessels is insufficient. 5 Space requirements Enough space for personnel to circulate around vessels and remove and sort samples. Small rooms (<16m 2 ) must be avoided as these require the highest rates of mechanical ventilation and can create difficulties in the correct positioning of alarms. Emergency egress routes must be maintained at all times. Enough space to manoeuvre and fill vessels safely and sufficient means of egress in the event of an emergency. Small rooms (<16m 2 ) must be avoided as these require the highest rates of mechanical ventilation and can create difficulties in the correct positioning of alarms. Enough space for the storage of the vessel out of traffic routes and away from emergency and fire escapes. Enough space to manoeuvre and fill vessels safely and sufficient means of egress in the event of an emergency. Enough space to manoeuvre and fill vessels safely and sufficient means of egress in the event of an emergency. Sufficient room to access instrumentation. A flat surface and enough room to manoeuvre vessels in and out safely. No ridges or kerbs at door threshold. Ideally covered with a canopy for weather protection. Imperial College Safety Department Page 29