Working in low oxygen-controlled atmospheres Risks and Prevention Measures Dr Michel Falcy, INRS FRANCE
Use of low O 2 -controlled atmospheres Nitrogenrefrigerated lorries Cryogenic facilities (sperm banks)
Use of low O 2 -controlled atmospheres Warehouses Data centres Libraries
A specific fire prevention technique Normal O 2 concentration: [19; 20.9] %v/v All combustibles can be characterised by an O 2 concentration under which they cannot catch fire. This O 2 concentration is always lower than 19% v/v but much higher than the concentration at which the fire smoulders or is extinguished. Continuous injection of nitrogen in order to maintain oxygen concentration < 19 %v/v Worker exposure to an oxygen-deficient atmosphere
O 2 from a toxicologist s point of view A dangerous gas > Carcinogenic > Toxic to the lungs > Immunotoxic Prevention > Exposure reduction But an essential gas > From a physiological point of view!
O 2 : percentage or quantity? The percentage is the same whether at sea level or at an altitude of 8,000 m The quantity is reduced by 2/3 Oxygen requirements > At rest 240 ml.min -1, i.e. 340 mg.min -1 > Maximum exercise 5 L. min -1, i.e. 71 g. min -1 intensity
Altitude and O 2 19%: 1,000 m 17%: 2,000 m 15%: 3,000 m 13%: 4,000 m Patients with heart failure cannot exceed 1,000 m without medical advice.
E.g.: Oxygen and Mount Everest O 2 % and N 2 % remain steady up to 21,000 m Produit: Oxygène (g/gmole) 32 Masse volumique (mg/m³) 274652 Pp[O²] (mm Hg) 160 Tn ( K) 298 Vmolaire (TPN) 24,45 Variation de la dose d'o 2 inspirée en fonction de l'altitude Altitude P T Cmax Cmax Dose % (m) (pi) (mm de Hg) ( K) (mg/m³) ppm (vol/vol) (mg) 0 0 160 298 274652 209851 2746515 100 2000 6605 125 285 225249 209851 2252486 82 4000 13210 97 272 183015 209851 1830152 67 6000 19815 74 259 147124 209851 1471239 54 8000 26420 56 246 116882 209851 1168825 43 10000 33025 42 233 91643 209851 916429 33
Risks for staff The more abruptly an environment becomes hypoxic, the more frequent and significant the symptoms: > Depressurisation in an airplane > Entry into a hypoxic area The significance of effects is also determined by the intensity of the physical effort and each individual s personal sensitivity.
Risks for staff The drop in oxygen partial pressure decreases the body s performance: > increase in fatigue, error rate, reaction time > decrease in balance, reasoning, and judgement Hard to compare with altitude sickness because in our case, > no variation in P atm > no adaptation phase > repeated variations in [O 2 ](entering/exiting) Recent studies on this exposure show a change in physiological data: > heart rate, oxygen saturation and blood pressure
Effects of hypoxia on the body Acute > Headaches > Tachycardia, increase in blood pressure > Mental disorders Chronic > Poorly known > Adaptation effects, in particular haematological adaptation > No knowledge on the effects of frequent changes in oxygen saturation > Overlapping with respiratory, cardiac or neurologic pathologies
Factors influencing clinical effects Existing pathologies > Respiratory > Cardiac > Haematological Physical effort Habituation
Effort levels level Low Moderate Intense examples Walking, checking inventory Light lifting, light maintenance work at ground level Climbing stairs and ladders, rapid handling Oxygen delivery required in the event of intense effort
Risks for staff Technical and organisational provisions in order to minimise exposure Need to implement fitness tests and medical follow-up for workers likely to intervene in these environments
Main provisions: general framework The oxygen concentration in the room must be as high as possible and evenly distributed. The technical, organisational and medical provisions will depend on the minimum concentration of oxygen that may be present in the room: Zone 1: [17;19[ %v/v Zone 2: [15;17[ %v/v Zone 3: [13;15[ %v/v Zone 4: < 13%v/v No permanent workstation in these zones Physical effort in these areas must be minimised (no intense effort).
Main provisions: general framework Tightness of the room Continuous measurement and display of [O 2 ] in the premises concerned and those adjoining them Access by electronic badge restricted to persons trained and followed medically by an occupational physician Permanent surveillance of people in the premises through a check point dedicated to monitoring and communication
Main provisions: general framework Use of a self-contained breathing apparatus (SCBA) or an oxygen supply device for all arduous work Record of work and length of stay for each worker ( exposure sheet ) Same measures for workers from outside companies
Main provisions: medical framework Questionnaire prior to the medical examination Before entering the zone for the first time Short questionnaire to establish the subject s health status Serves to determine the medical examinations
Main provisions: medical framework Medical exams and fitness test > Before entering the premises > Performed regularly Additional or subsequent exams based on the occupational physician s advice (taking into account the work load) The fitness test will specify the zones in which the employee may work.
Main provisions: medical framework Stages in determining fitness > Medical history > Medical exam > According to zones and levels of physical effort Additional exams Think of using a SCBA or an oxygen supply device (zones 2, 3 and 4)
Medical exams Medical history > Blood diseases > Heart diseases > Circulatory diseases > High blood pressure > Respiratory disorders > Damage to the nervous system > Metabolic disorders (diabetes) Clinical exam > Lungs > Heart and blood vessels > Abdomen (liver and spleen) > Neurological exam
Additional exams Laboratory exams > Blood count, blood glucose level, creatinine level, ALT, Gamma-GT Spirometry > At least FEV1 and flow-volume loop EKG > Rest, effort > Recommended by certain experts for oxygendeficient environments
Other additional exams More thorough depending on the result of the initial exams A check-up in a specialised health department might be necessary > Occupational disease consultation > Sports medicine consultation
Instructions for zone 1 Main prevention principles Limit physical effort Screening for: > Cardiopathy > Cardiovascular disease > Respiratory diseases > Blood diseases > Neurological disorders
Instructions for zones 2 and 3 Idem zone 1 Health questionnaire Short stay Traceability of stays Preliminary medical exam Additional check > Exercise EKG and rest EKG (with and/or without hypoxia) Use of a SCBA or an oxygen supply device No pregnant women
Instructions for zone 4 Idem zone 1, 2, 3 Use of a SCBA or an oxygen supply device Medical exam for the use of a SCBA or an oxygen supply device
Conclusions Hypoxic situations are rare and often predictable Poor knowledge of long-term effects Should not be considered as habitual workstations Need for technical and medical prevention measures adapted to employees and situations