6a.risk, safety & accident
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Chapter 5
Risk, Safety and Accidents
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Risk, Safety and Accidents
The most important duty of an engineer
is to protect the safety and well-beingof the public
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Definitions
Safety is defined as the
freedom from damage,injury or risk
Risk is defined as thepossibility of sufferingharm or loss, similarto danger
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Linked
The definitions of safety and risk are linked
We engage in riskybehavior when wedo something that isunsafe
Something is unsafeif it involvessubstantial risk
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Factors in Risk and Safety
Whether something is safe or free of risk issubjective and depends on many factors
Voluntary vs. involuntary riskMany consider something safe if
the risks involved have been fullydisclosed to them beforehand
Short vs. long-term consequences
Something that might cause a short-lived
disability or illness often seems safer thansomething that could result in a
permanent disability
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Factors in Risk and Safety
Expected probability
1 in 1,000,000 chance of severeinjury is often considered to be anacceptable risk, whereas a 50:50chance of fairly minor injury may be
judged as unacceptable Reversible effects
Things often seem less risky if
the bad effects are ultimatelyreversible
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Factors in Risk and Safety
Delayed vs. immediate effects
An activity whose harmful effect is
delayed for many years may seem
less risky than something with animmediate effect
Safety and risk are subjective, the engineer and
his/her company must use their professionaljudgment to determine whether a project can besafely implemented
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Four Criteria for Safe Design
Designs must complywith applicable laws
A design must meet the standard of accepted engineeringpractice. If it is accepted practice to go further thanregulations require, designs which do not meet the de factoindustry standards will be rejected by the public
Alternative designs that arepotentially safer must beexplored
The engineer must attempt to foresee potentialmisuses of the product by the consumerand must design to minimize the risksassociated with such misuse
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Designing for Safety
Define the problem, including the needs,requirements and constraints
Generate several different solutions to the
problem Analyze each solution to determine the pros
and cons of each
Test the solution
Select the best solution
Implement the chosen solution
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Risk-Benefit Analysis
Risks and benefits of aproject are assigned
dollar amounts
Most favorable ratiobetween risks and
benefits is sought
This is often a difficult task because
It is often difficult to assign appropriate dollar amounts Technique can be misused by dishonest and subjective
assignment of costs
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Accidents
We define three types of accidents
Procedural
Engineered
Systemic
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Procedural Accidents
Most common accident category
Often caused by a bad
choice or failure to followregulations or establishedprocedures
Can be reduced through
increased training, moresupervision, new laws orregulations, or closer scrutiny(teliti- cermat) by regulators
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Engineered Accidents
Caused by flaws in the design of a product or systemand include
Failure of materials
Devices that do not perform as expected Devices that do not perform well under all
circumstances encountered
Engineered failures shouldbe anticipated during thedesign phase and shouldbe caught and correctedduring testing
Engineered accidents canbe reduced by testingthroughout the entirerange of possibleoperating conditions
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Systemic Accidents
The hardest accident type tounderstand and control
Characteristic of complex
technologies and systemsand within the complexorganizations required fortheir operation
A series of minor mistakes orinsignificant factors, can, ifthey occur under certain
circumstances havecatastrophic consequences
Can be reduced by payingscrupulous (cermat)attention to detail and byresisting the urge toignore procedures andaccepted engineering
practice
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Conclusion
Definitions of safety and risk
Factors in determining safety and risk
Criteria for safe design Designing for safety
Accidents
Procedural Engineered
Systemic
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