3 Inherently Safer Background Recognized in 1970’s for chemical industry –Trevor Kletz, “What You Don’t Have Can’t Leak” 1996: CCPS Concept Book –Inherently Safer Chemical Processes- A Life Cycle Approach
4 American Institute of Chemical Engineers Center for Chemical Process Safety Concept Book (1996)
5 Inherent Safety Inherent - “...existing in something as a permanent and inseparable element, quality, or attribute.” American College Dictionary
6 What is inherently safer design? Inherent - “existing in something as a permanent and inseparable element...” –safety “built in”, not “added on” Eliminate or minimize hazards rather than control hazards More a philosophy and way of thinking than a specific set of tools and methods –Applicable at all levels of design and operation from conceptual design to plant operations “Safer,” not “Safe”
7 Inherently Safer Design Strategies StrategyExamples Substitute Replace material with a less hazardous substance. Minimize Use smaller quantities; eliminate unnecessary equipment; reduce size of equipment or volumes processed. Moderate Use less hazardous conditions, a less hazardous form of material or facilities which minimize the impact of a release. Simplify Design facilities which eliminate unnecessary complexity and make operating errors less likely.
8 Substitute Chlorine for Cooling Tower Water Treatment –5 1-tonne cylinders per tower, manifolded, 1 hooked up at a time. Replaced with bleach solution in water –Eliminated downwind chlorine exposure from leak –Provided better control for water treatment
9 Substitution - Refrigeration Many years ago (pre-1930) –Toxic, flammable refrigerants Ammonia, light hydrocarbons, sulfur dioxide Quantity – often several kilograms Inherently safer alternative (1930s) –CFCs Discovery of environmental problems (1980s) –“Green” alternatives include light hydrocarbons –Require re-design of home refrigerators to minimize quantity of flammable hydrocarbon (currently as little as 120 grams of hydrocarbon refrigerant)
11 Inherently safe? No, but inherently safer. Hazards are primarily flammability, corrosivity from sulfuric acid catalyst for the esterification step, small amounts of acrolein as a transient intermediate in the oxidation step, reactivity hazard for the monomer product. Propylene Oxidation Process Alternate Reaction Chemistry
12 Minimize Houston Plant had 7 multi-tonne Ammonia Blimps – why? –Heavy user of ammonia –Formerly had ammonia production plant, but –Ammonia now comes by pipeline Post-Bhopal: –Reduced inventory to 50% of 1 blimp. –1 blimp in service, 1 undergoing inspection –Other blimps converted to N2, salt, H2SO4 service –Reduced maintenance costs
13 Moderate Dilution Refrigeration Less severe processing conditions Containment –Better described as “passive” rather than “inherent”
14 Dilution Aqueous ammonia instead of anhydrous Aqueous HCl in place of anhydrous HCl Sulfuric acid in place of oleum Wet benzoyl peroxide in place of dry Dynamite instead of nitroglycerine
17 Less severe processing conditions Ammonia manufacture –1930s - pressures up to 600 bar –1950s - typically 300-350 bar –1980s - plants operating at pressures of 100-150 bar were being built Result of understanding and improving the process Lower pressure plants are cheaper, more efficient, as well as safer
18 Inherently Safer Containment Dikes What physical parameters control evaporation from a spilled liquid in a storage tank containment dike?
25 Conflicts and Tradeoffs “It’s always a trade-off”
26 Some problems The properties of a technology which make it hazardous may be the same as the properties which make it useful –Airplanes travel at 600 mph –Gasoline is flammable Any replacement for gasoline must have one similar characteristic - the ability to store a large quantity of energy in a compact form –a good definition of a hazardous situation –Chlorine is toxic Control of the hazard is the critical issue in safely getting the benefits of the technology
27 Multiple hazards Everything has multiple hazards –Automobile travel velocity (energy), flammable fuel, exhaust gas toxicity, hot surfaces, pressurized cooling system, electricity...... –Chemical process or product acute toxicity, flammability, corrosiveness, chronic toxicity, various environmental impacts, reactivity.......
28 What is the hazard of concern… …if you live on top of a hill in Detroit? …if you live on the ocean front at the shore? Which is inherently safer?
29 At what phase of design should engineers and chemists consider inherently safer design? My answer – at all levels! Inherently safer design is not a meeting, or a review session. Inherently safer design is a way of thinking, a way of approaching technology design at every level of detail – part of the daily thought process of a chemist, engineer, or other designer as he goes about his work.
30 Questions a designer should ask when he has identified a hazard In this order 1.Can I eliminate this hazard? 2.If not, can I reduce the magnitude of the hazard? 3.Do the alternatives identified in questions 1 and 2 increase the magnitude of any other hazards, or create new hazards? (If so, consider all hazards in selecting the best alternative.) 4.At this point, what technical and management systems are required to manage the hazards which inevitably will remain?
31 Better may be harder to invent “There are two ways of dealing with this problem: one is complicated and messy, and the other is simple and elegant. We don’t have much time left, so I’ll show you the complicated and messy way.” - Richard P. Feynman Nobel Prize winning physicist, discussing approaches to understanding a physics problem
32 Reference Slides For inherently safer design
33 Process Safety Risk Management Strategies Inherent –Eliminate or modify the hazard and/or risk by employing one of four strategies of substitution, minimization, moderation, simplification. Passive –Minimize the hazard by process and equipment design features which reduce either the frequency or consequences of the hazard without the active functioning of any device. Active –Using controls, safety interlocks, and emergency shutdown systems to detect and correct process deviations. Procedural –Using operating procedures, administrative checks, and emergency response to prevent incidents, or to minimize the effect of an incident.
37 For More Information - Books Inherently Safer Chemical Processes - A Life Cycle Approach, American Institute of Chemical Engineers, New York, 1996. INSET Toolkit, Commission of the European Community, 1997. –available for free download from AEA Technologies: http://www.aeat-safety-and-risk.com/html/inset.html Guidelines for Engineering Design for Designing Solutions for Process Equipment Failures, American Institute of Chemical Engineers, New York, 1998. Kletz, T. A., Process Plants - A Handbook for Inherently Safer Design, Taylor and Francis, London, 1998.