3 rd Year Design Module Scope

Transcription

1 LOSS PREVENTION & Process Safety PROCESS HAZARDS ANALYSIS -3 rd Year Design Module - 3 rd Year Design Module Scope Hazard Identification In the Process 1. Identify the major hazards that are present 2. Inherent Safety - Comment on ways to eliminate or reduce the hazards PHA 3 rd year design Module scope Hazard Consequence Identification Analysis Facility Siting Human Factors Hazard Reviews Risk Analysis / Recommendations

2 Agenda Today What is a PHA, Why do we do them? Important background concepts to understand before you can do a PHA What is a hazard, what is a hazardous event? What types of fires and explosions are there? Fireball, pool fire, jet fire, physical explosion, chemical explosion, BLEVE What is risk, how do we calculate it? The Hazard Identification Process Further Reading Inherently Safer Design WHY PHA s Ethically -We all want to return to our homes and family at night and likewise for our fellow employees Financially - Accidents can have serious effects on the financial viability of a company, or even the right to operate. Purpose: To identify elements of a process that exceed acceptable risk

3 What is A PHA? The PHA process: 1. Identifies the hazards in the process 2. Assesses the risk of the hazard 3. Where necessary, makes recommendations to reduce or minimize the risk Exercise What Hazards do you think we have in our process?

4 What is a Hazard? Definitions What is a hazard? A hazard is anything with the potential to cause harm e.g. the presence of a elevated scaffolding that people can fall off. What is risk? A risk is the likelihood that a hazard will cause a specified harm to someone or something e.g. if the guard rail is missing it is likely that a construction worker will fall off the scaffolding and break a bone. What is risk management? Risk Management is a process that involves assessing the risks that arise in your workplace, putting sensible health and safety measures in place to control them and then making sure they work in practice. What is risk assessment? A risk assessment is nothing more than a careful examination of what, in your work, could cause harm to people, so that you can weigh up whether you have taken enough precautions or should do more to prevent harm. Source: What is a Hazard? An inherent physical or chemical characteristic that has the potential for causing harm to people, the environment, or property (CCPS, 1992). Hazards are intrinsic to a material, or its conditions of use. Examples Phosgene - toxic by inhalation Acetone - flammable High pressure steam - potential energy due to pressure, high temperature Source: Inherently Safer Design by Harry J. Toups Available on the Safety and Chemical Engineering Education website ( CCPS -Center for Chemical Process Safety -

5 What is Risk? Risk = Severity of the Event s Consequences X Frequency of the Event Consequences Frequency / Probability Frequency High Class 1 Class 3 Class 3 Moderate Class 1 Class 2 Class 3 Very Low Class 1 Class 1 Class 1 Low Moderate High Consequences For more information on what is considered acceptable risk refer to Chemical Engineering Magazine, Sept 2007 The Hazard Mechanism Event Timeline Temp. Control Valve TV-100 Sticks Cooling Water Control is lost Tempera ture of Reactor Rises Auto decomposi tion of material X occurs Vessel Ruptures Explosion causes damage to surrounding areas high probability of injury and large financial costs HazardEvaluation Hazard Identification Consequence Analysis The hazard here is the explosion it has the potential to injure someone The hazardous property of material X is that it can undergo autodecomposition and cause a vessel to rupture

6 Types of Hazards Fire (Radiation) Explosion (Physical Explosion, Chemical Explosion, BLEVE) Pressure Wave, Fireball, Missiles Toxic Release Toxic Concentrations - Indoor, Downwind Others anything that can cause a serious impediment to continuing business (i.e. Injury, noise, odour,..) Fire Triangle FIRE Flammable Range LFL, UFL Flam. Range 0 % VOL 100 % VOL LEL, UEL Oxidizer Ignition Source (they come for free)

7 Fire - Ignition Heat autoignition temperatures flash point Open Cup Electrical (spark, static, lightning ) Open Flames (welding, fired heaters, flares) Fire - Flammability Limits Acetone Acetylene Carbon Monoxide Cyclohexane Ethylene Methane (Nat Gas) Propane LEL UEL (% vol) * * 100 % at pressures > 7 MPa (7,000 kpa = 1000 psig)

8 Hazard Idenfication Hazard identification Is a flammable gas with inerts (i.e. CO, CO2, H2O, H2) flammable or not? Non flammable Gas using N2 As inert image: Consequence Spreadsheet - Determination of Gas Flammability Combustible Component Name concentrati on, %vol LEL, % vol frac of Total Combustib les fraction / LEL Carbon Monoxide Step 2. Hydrogen Lower Flammability Limit, % vol 3.81 % Methane Concentration of Combustibles 1.99 % Ethylene Component placeholder - - Step 3. Is this a Combustible Mixture in Air or by itself? Component placeholder - - No * Component placeholder - - Component placeholder - - * If concentration of combustibles is less than the Lower Flammability Limit Component placeholder - - then when released to atmpsophere and diluted, it will remain below the Component placeholder - - flammabilty limit. Component placeholder - - Component placeholder - - Note: Gases must have 'similar' flammability characteristics for Total combustibles 1.99 % vol in mixture 1.00 Le Chatelier's Rule to be applicable Note: Composite Upper Flammabiliity may be Non Combustible calculated in 17 of Air - 0O2 similar manner. CO N2 -

9 Fires - Pool Fire Fires - Vapour Cloud Fire aka Flash Fire Flash Fire has no significant overpress ure (like a BBQ Puff)

10 Fires - Jet Fire Explosions - Vapour Cloud Difference between Fire and Explosion is the occurrence of Overpressure Overpressure causes significant harm Conditions Required Development of Gas Cloud (delayed ignition) Ignition Source Gas Concentration in Range for Detonation Oxidizer? Detonation 0 % VOL 100 % VOL

11 Vapour Cloud Explosion time Vapour Cloud Explosion Confined Spaces (building, congested piping,..) provide increased overpressure Possible 23 of Confined Space

12 BLEVE BLEVE (Boiling Liquid Expanding Vapour Cloud Explosion Note: Does not necessarily involve a flammable fluid inside the vessel Water Boiler BLEVE s are possible 1. Vessel isolated no where for excess pressure to go 2. Flame Impingement -Hot spot (no liquid) Metal cooled by liquid boiling (vessel safe here) Explosion - Physical The higher the pressure at time of vessel failure, the bigger the blast wave! Isentropic expansion calculation 25 of

13 Gas Releases Neutrally Buoyant Gas Plume Wind 39 of 43 Gas Releases Neutral Buoyant Puff Release Wind Time & Movement 39 of 43

14 Gas Releases Heavy Gas Plume Wind 39 of 43 Fluid Properties vs OP. Conditions i.e. MeOH Present At T s above flash point Consequence Analysis Process Hazards Analysis Hazard Identification Hazards To Look For: -Fire -Explosion -Toxic Release MeOH must get out of process (loss of containment) 3 rd year design module stops here Hazard Evaluation Assume 2 minute release, 30 cu ft of material is released Consequence Analysis shows windows are broken out to 100 ft Loss of HAZOP Containment Checklist {other review } Scenario 1: Loss of coolant Scenario 2: Drain Valve is opened On Site Consequences Probability = likely based on mechanism Consequence Analysis MeOH released is flashing Risk Analysis = Unacceptable Recommendations Remove valve Provide locks for valve Vap released creates vap cloud Liq release causes pool fire {follow same steps as vap release}

15 Hazard Identification Is there explosion, fire, or toxic release potential? Properties of Materials Reactive - Mix wrong proportions, abnormal chemicals, temperature or pressure excursions Flammable Explosive Toxic - humans, ecology Heavier or lighter than air Large Quantities Properties of the Process High Operating Pressure, Gaseous or Liquid Vents to Atm., Operating Temp > Flash Pt. Hazard Identification Material Properties Flammability Limits Autoignition Temp Toxicity Stability Quantity / Inventory Process Properties Pressure Gas Phase / Liquid Phase Vents to Atmosphere Hazards Fire (jet, pool, flash) Explosion (chemical, BLEVE, Physical) Toxic Release Other (anything that can cause injury or business interruption)

16 Example Propane Tank MSDS Sheet Toxicity - Definitions Definitions: PAC Protective Action Criteria TEEL Temporary Emergency Exposure Limit ERPG Emergency Response Planning Guideline Level 0 acceptable Level 1 noxious Level 2 People incapacitated can not escape Level 3 - Death

17 Propane - Toxicity Conclusion PAC-2 conc = 1.7% vol in air therefore relatively non toxic as compared to Consistent with MSDS health rating of 1 Example - Hazard Identification Material Property Hazards As per previous slide low toxicity hazard LEL / UEL for Propane are: 2.5% and 9.5% The material is a Fire and/or Explosion Hazard The propane is single component, therefore no test for multi component flammability w spreadsheet Reactivity: Propane does not undergo autodecomposition or autopolymerization, or other reactive decompositions

18 Operating Conditions Operating Condition Hazards An oxidizer is not normally present inside the equipment Abnormal operation (addition of an oxidizer) is required for fire/explosion hazard to occur Fires and explosions can occur if there is loss of containment (propane getting out of process) Fires and explosions can occur if an oxidizer is accidentally in the equipment Example - Hazard Identification Assuming our example system operates at 40 C, 20 bar (propane is liquid) & no oxidizer is present Hazards of Propane in our process are: The propane is being operated above it s flash point (-105 C), and when released it will remain above it s flash point. Therefore, leaks plus an ignition source are likely to result in a fire or explosion hazard. Two phase T > Flash Point

19 Example - Hazard Identification Based on the flash calculation Both a liquid and vapour are present Both phases are combustible Vapour can form a fire/explosion Liquid can form a pool fire Liquid is likely to evaporate relatively quickly due to very high vapour pressure but depends on temperature of ground (winter/summer) The liquid is very cold cold burn hazard is possible (probably localized and not the primary hazard) Example - Hazard Identification Nowhere is the temperature above the autoignition temperature, therefore all leaks will require an ignition source There is likely to be a delay between when the leak initially occurs and when the ignition occurs, thus a buildup of flammable material would occur, thus a flash fire or explosion is possible If the material was above the autoignition temperature what type of hazard do you think would occur if there was a leak?

20 Example - Hazard Identification The vapour density is greater than one, therefore leaks will hug the ground Ignition sources are more likely to be found Toxic effects to people are more likely to occur Operating Condition Hazards Other hazards: Propane storage tank is normally held in steel storage tanks (isolated) with vapour space above liquid. Therefore BLEVE hazard is possible.

21 Part 1 - Hazard Identification Chemical Interaction Matrix Propane Water Steel Propane Water Steel yes none X none yes X Triple/Multiple combinations: None Part 1 - Hazard Identification Chemical Interaction Matrix Therefore, no reactivity hazard exists, but Corrosion may be a mechanism for failure.

22 What Can Happen Loss Of Containment Events can occur inside equipment and lead to explosions or fires Runaway Reactions, explosions due to chemical properties or oxygen ingress, fires The worst ones cause the equipment to fail and the following Events can occur outside equipment A release of toxic gas A release of flammable gas or liquid A sudden release of pressure physical explosion Explosions occur quickly and send a shock wave and missiles that destroy and kill Pool and jet fires occur more slowly and usually only damage equipment can cause secondary failures Toxic Releases Ways to Reduce Hazards Inherently Safe Designs seek to reduce or eliminate the hazard from the process. What you don t have, you can t lose Strategies: Minimize Moderate Substitute Simplify For more information refer to Inherently Safer Design by Harry J. Toups Available on the Safety and Chemical Engineering Education website (

23 3 rd year Design Hazard Identification List the Materials involved, Flash Point, Autoignition, LEL, UEL, Compare to Process operating temperature Make Conclusions - Do materials posses the potential to create a fire, explosion, BLEVE, or toxic hazard (internally inside the process and/or only in event of a release) May need to use Flammability Test.xls spreadsheet. May need to do a flash calculation List the Process operating conditions. Is a physical explosion or BLEVE possible. Review slides on Inherent Safety and make some recommendations that would make our system more safe. Ultimately make a conclusion whether you think the hazards are acceptable or not. If not, what should be done to make them acceptable.