Introduction to Process Safety

1. Introduction to Process Safety

2. To know is to survive and to ignore fundamentals is to court disaster H.H. Fawcett and W.S. Wood, Safety and Accident Prevention in chemical operation, New York, Wiley, 1984.

3. Three important terminologies • Safety or loss prevention – the prevention of accident through the use of appropriate technologies to identify the hazards of a chemical plant and eliminate them before accident occurs • Hazard – a chemical or physical condition that has the potential to cause damage to people, property or the environment • Risk – a measure of human injury, environmental damage or economic loss in terms of both the incident likelihood and the magnitude of the loss or injury

4. Definition of Risk • Extent of Damage • Probability of Fatality • Monetory Losses • Likelihood of failure Risk = Severity x Likelihood

5. Risk is expressed in as Rating • Rating is typically • simple to use and understand • Not require extensive knowledge to use • Have consistent likelihood ranges that cover the full spectrum of potential scenarios • In applying risk assessment • Clear guidance on applicability is provided • Detailed descriptions of the consequences of concern for each consequence range should be described • Have clearly defined tolerable and intolerable risk levels • Following risk assessment • Scenarios that are at an intolerable risk level can be mitigated to a tolerable risk level on the matrix • Clear guidance on what action is necessary to mitigate scenarios with intolerable risk levels are provided

6. Example of a Consequence Range

7. Example of Likelihood Ranges

8. Example Risk Ranking Categories

9. Risk Matrix Risk = Probability of occurrence x Consequence of occurrence

10. Guidelines for Risk Mitigation

11. Accident and Loss Statistics • Accident and loss statistics are used to measure the effectiveness of safety programs. • Among statistical methods used to characterize accident and loss performance : • - OSHA (Occupational Safety and Health Administration, USA) incidence rate • - Fatal accident rate (FAR) • - Fatality rate or deaths per person per year • These methods report number of accidents and/or fatalities for fixed number of workers during specified period.

12. OSHA Incidence Rate • based on cases per 100 worker years. • 1 worker year = 50 work weeks/yr x 40 hrs/weeks = 2000 hrs • based on 200,000 hrs worker exposure to hazard • two types of calculation (1) based on injuries and illness (2) based on lost workdays • OSHA (1) = number of injuries & illness x 200,000 / total hrs work by all employees during period covered • OSHA (2) = number of lost workdays x 200,000 / total hrs work by all employees during period covered

13. Fatality Accident Rate • Used by British chemical industries. Data is widely available in literature. • Fatalities based on 1000 employees working their lifetime. Employees assumed working total 50 years (108 working hrs). • FAR = number fatalities x 108 / total working hrs by all employees during period covered • Fatality rate = number of fatalities per year / total number of people in applicable population • FAR can be converted to fatality rate (or vice versa) if number of exposed hours is known. • OSHA incidence rate cannot be converted to FAR or fatality rate because it contains both injury & fatality information.

14. Example • Given FAR =2. If employee works 8 hr shift 300 days per year, compute fatality rate • Fatality rate = 8 hrs/day x 300 days/year x 2 deaths/108 hrs = 4.8 x 10-5 death per person per year • More rock climbers are killed travelling by car than are killed during rock climbing. Is this statement supported by statistics? • From data, travelling by car, FAR=57, rock climbing, FAR = 4000. • Rock climbing produces more fatalities per exposed hrs but spend more time(exposed hrs) travelling by car. Think about this...

15. Example

16. Tolerable Risk • Risk cannot be eliminated entirely. • Every chemical process has a certain amount of risk associated with it. • At some point in the design stage someone needs to decide if the risks are “tolerable". • Each country has it owns tolerability criteria. • One tolerability criteria in the UK is "as low as reasonable practicable" (ALARP) concept formalized in 1974 by United Kingdom Health and Safety at Work Act. • Details will be treated later (Topic:QRA)

17. In life, there is always some risks… • There is no such thing as zero risk • All activities involve some risks • The issue is at level should we tolerate these risks…

18. Tolerability Criteria • This framework is represented as a three-tier system as shown in figure. It consists of several elements : • (1) Upper-bound on individual (and possibly, societal) risk levels, beyond which risks unacceptable. • (2) Lower-bound on individual (and possibly, societal) risk levels, below which risks are deemed not to warrant regulatory concern. • (3) intermediate region between (1) and (2) above, where further individual and societal risk reductions are required to achieve a level deemed "as low as reasonably practicable (ALARP)".

19. ALARP Criteria INTOLERABLE LEVEL (Risk cannot be justified on any ground) TOLERABLE only if risk reduction is impracticable or if its cost is grossly disproportionate to the improvement gained THE ALARP REGION (Risk is undertaken if benefited is desired) TOLERABLE if cost of reduction would exceed the improvement gained BROADLY ACCEPTABLE REGION

20. Causes of Accidents and Incidents Incidents and Accidents are caused by either unsafe behaviours (substandard practice) and/or unsafe conditions (substandard designs). Unsafe behaviours are handled by Occupational Safety Program, Unsafe conditions are managed through Process Safety Programs.

21. Inherent Safety

22. Inherent Safety • To make the concept more understandable, the following four words have been recommended to describe inherent safety • Minimise (intensification) • Substitute (substitution) • Moderate (attenuation and limitation of effects) • Simplify (simplification and error tolerance)

23. Minimise (example) • Change from larger batch reactor to smaller continuous reactor • Reduce storage inventory of raw materials • Improve control to reduce inventory of hazardous intermediate chemicals • Reduce process hold-up

24. Substitute (example) • Use mechanical pump seals vs packing • Use welded pipe vs flanged • Use solvent that are less toxic • Use mechanical gauges vs mercury • Use chemicals with higher flash point, boiling points, and other less hazardous properties • Use water as heat transfer fluid instead of hot oil

25. Moderate (example) • Use vacuum to reduce boiling point • Reduce process temperature and pressure • Refrigerate storage vessel • Dissolve hazardous materials in safe solvent • Place control rooms away from operation • Operate at conditions where runaway reactions are not possible • Separate pump rooms from other rooms • Barricade control rooms and tanks

26. Simplify (example) • Keep piping systems neat and visually easy to follow • Design control panels that are easy to comprehend • Design plants for easy and safe maintenance • Pick equipment with low failure rates • Separate systems and controls into blocks that are easy to comprehend and understand • Label pipes for easy ‘walking the line” • Label vessels and controls to enhance understanding • Add fire and explosion resistant barricades

27. Inherent Safety Concept • Reduce the risk at early stage of design

28. Process development Project sanction Conceptual Design, engineering, construction Hand over operation Stage 1 Concept Stage 2 Process design Stage 3 Detailed Engineering Stage 4 Construction Stage 5 Pre- Commis sioning Stage 6 Post- commis sioning PROJECT PHASE Safety issues must be embedded within all project life-cycle Relationship of six-stage process study system to project life-cycle

29. LOPA Checklist HAZOP RR PHR Method Used What-if FMEA FTA ETA Many hazard identification technique can be used at appropriate cycle

30. Hazard identification technique and project phase