Introduction to Inherently
Safer Concepts
Presented by: Kathy Kas, PE
Developed by: Art Dowell, PE
Risk Management Services
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Why Inherently Safer Design?
Allentown, PA, 1999
Flixborough, UK, 1974
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Pasadena, TX, 1989
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
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American Institute of
Chemical Engineers
Center for Chemical Process
Safety
Concept Book (1996)
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Inherent Safety
• Inherent - “...existing in something as a
permanent and inseparable element, quality, or
attribute.”
American College Dictionary
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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”
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Inherently Safer Design Strategies
Strategy
Examples
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.
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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
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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)
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Reaction Chemistry - Acrylic Esters
Reppe Process
•
•
•
•
•
Ni(CO )4
CH  CH + CO + ROH
 CH 2 = CHCO2 R
HCl
Acetylene - flammable, reactive
Carbon monoxide - toxic, flammable
Nickel carbonyl - toxic, environmental hazard (heavy
metals), carcinogenic
Anhydrous HCl - toxic, corrosive
Product - a monomer with reactivity (polymerization)
hazards
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Alternate Reaction Chemistry
Propylene Oxidation Process
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Catalyst
 CH 2 = CHCO2 H + H 2 O
CH 2 = CHCH 3 + O2
2
CH 2 = CHCO2 H + ROH
H+
 CH 2 = CHCO2 R + H 2 O
• 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.
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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
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Moderate
•
•
•
•
Dilution
Refrigeration
Less severe processing conditions
Containment
– Better described as “passive” rather than “inherent”
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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
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Cent
Conce
28%
Aqueous
Ammonia
0
0
Effect of dilution
Distance, Miles
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Centerline Ammonia
Concentration, mole ppm
20,000
(B) - Release Scenario:
2 inch transfer pipe failure
10,000
Anhydrous
Ammonia
28%
Aqueous
Ammonia
0
0
Distance, Miles
1
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Impact of refrigeration
Monomethylamine
Storage
Temperature
(°C)
10
3
-6
Distance to
ERPG-3 (500 ppm)
Concentration,
km
1.9
1.1
0.6
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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
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Inherently Safer Containment Dikes
• What physical parameters control evaporation
from a spilled liquid in a storage tank
containment dike?
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Liquid Pool Behavior
Pool spreads until it reaches dyke wall
or its minimum thickness
wind
boiling
heat transfer
•
evaporation mass
transfer
Chlorine storage
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Liquified Gas storage example
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Simplify
• Eliminate unnecessary complexity to reduce
risk of human error
– QUESTION ALL COMPLEXITY! Is it really
necessary?
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Simplify
Controls on a stove
From Don Norman, “Turn Signals are the Facial Expressions of Automobiles”
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Simplify
Did somebody really do this?
North Train
Equipment
South Train
Equipment
Plant
AAA
1
AAA
2
South Train
Controls
N
AAA
1
AAA
2
North Train
Controls
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Conflicts and Tradeoffs
“It’s always a trade-off”
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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
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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.......
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Which is inherently safer?
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?
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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.
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Questions a designer should ask
when he has identified a hazard
In this order
1.
2.
3.
Can I eliminate this hazard?
If not, can I reduce the magnitude of the hazard?
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?
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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
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Reference Slides
• For inherently safer design
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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.
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Layers of Protection
RESPONSE
LIMITATION
BARRIER
MITIGATIVE
PREVENTIVE
SUPERVISORY
CONTROL
INHERENTLY SAFER
DESIGN
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Inherently Safer Approach to Analyzing
& Managing Process Risks
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Continued
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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.
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