6a.risk, safety & accident

8/2/2019 6a.risk, Safety & Accident

1/15

Chapter 5

Risk, Safety and Accidents


2/15

Risk, Safety and Accidents

The most important duty of an engineer

is to protect the safety and well-beingof the public


3/15

Definitions

Safety is defined as the

freedom from damage,injury or risk

Risk is defined as thepossibility of sufferingharm or loss, similarto danger


4/15

Linked

The definitions of safety and risk are linked

We engage in riskybehavior when wedo something that isunsafe

Something is unsafeif it involvessubstantial risk


5/15

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


6/15


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


7/15


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


8/15

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


9/15

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


10/15

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


11/15

Accidents

We define three types of accidents

Procedural

Engineered

Systemic


12/15

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


13/15

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


14/15

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


15/15

Conclusion

Definitions of safety and risk

Factors in determining safety and risk

Criteria for safe design Designing for safety

Accidents

Procedural Engineered

Systemic

6a.risk, safety & accident

Documents