×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

What does "safe" mean to you?
6

What does "safe" mean to you?

What does "safe" mean to you?

(OP)
As engineers, it is expected that we hold paramount the safety of the general public.  Everyone has heard the expression "safety first."

One definition for "safe" (Webster's) is "free from harm or risk."  I would argue that no product or process whatsoever is completely free from harm or risk.

So how do we really decide if a product or process is safe?  Obviously, at some point, you have to accept some level of risk.  How do we decide what level of risk is acceptable?

With some products or processes, there are codes or standards that must be met for safety, which can make our jobs easier.  But did you ever stop to think where those codes and standards came from?  Who developed them and what was their reasoning?  More importantly, do you agree with their reasoning?

Anyway, before I ramble too much (maybe it's too late), I'd be interested to hear (read) peoples' thoughts on this.

Haf

RE: What does "safe" mean to you?

3
What's sometimes done, as in the case of the Pinto, is a calculated cost-benefit margin.

In other cases, such as the Space Shuttle, there was a calculated and acceptable level of risk.

In yet other cases, such as when we speed or do something stupid on the freeway, no consideration is taken for level of risk, even though we may consciously be aware of the risk.

In yet other cases, such as when we wake up, we simply ignore the risk and the possibility of risk altogether.

TTFN

RE: What does "safe" mean to you?

Nice post IRstuff.

RE: What does "safe" mean to you?

To IRstuff's post I would add the caveat of doing the cost-benefit/risk analysis based upon an established performance envelope.  Using the Pinto as an example, I would contend that it is reasonable to assume that auto accidents may occur.  Therefore, the design should be capable of accommodating accidents to a certain level of severity.  While I do not know the requirements for the Pinto, it appears that it will be remembered historically as insufficient.  If the explosions and fires had been caused by accidents with semi's or trains, perhaps a different result.

The shuttles appeared to be one case of use outside of the established performance envelope (launch in conditions too cold for the O-rings seals), and a case of reality proving that "theory" is exactly that.  Theory: Foam impact should not cause damage.  Modified Theory: Foam impact might cause damage.  Reality:  Self explanatory.

Note that these are my opinions only.  For any design, there is a need to accomodate an expected performance envelope.  With in this realm, we are bound ethically.  Use or misuse outside of this envelope is beyond the control of designers and engineers.

Regards,

RE: What does "safe" mean to you?

You are conflating two different accidents.

The O ring problem ,as Feynman showed, was that the system was routinely being stressed beyond its design limits.

I don't think anyone has really demonstrated what happened with the foam, yet, to the same sort of standard.




Cheers

Greg Locock

RE: What does "safe" mean to you?

Haf,

I think your post implies the engineer knows the risks associated with the product or process. There is a clear responsibility for the people who use the product or are employed to operate the process are advised of the risks.

There are plenty of court cases that determined this did not happen. That's not answering your question, but ensuring people know the risks is part of the equation?

J.

RE: What does "safe" mean to you?

Whether or not we agree with the reasoning is insignificant.  The code or standard is now law and we must abide by it.

I believe a good example of this is the OHSA in Ontario.  The approach is taken that an operator will at some point go out of their way to do something that will injure themself.  The safety of a machine being operated is approached from this standpoint and every effort is made to ensure that it is impossible for the operator to injure themself on the equipment even if they are trying to injure themself.
ie. guarding must go low enough and light curtains mounted low enough that an operator cannot reach under them and touch moving equipment. The opposite is true as well.

In our manufacturing environment if I say "well it looks safe enough..." I know more work needs to be done.

In terms of the general public I believe the term is called due diligence.  As an Engineer you are responsible for assuming that an item will be pushed beyond its design limits by the general public in its normal application.  You are expected to design for this (translate as factor of safety).

For unusual applications not forseen by the Engineer you sometimes must demonstrate that it should have been obvious that the item would fail in this application (translate as the guy was an idiot for trying that and should have consulted an Engineer).  

The second item rarely occurs but there have been two cases in which it was required to demonstrate that the individual should have known to consult with an Engineer.

All cases are relevant to Ontario Law and may not be the same where you live.

So safe to me means Darwin is spinning in his grave.

RE: What does "safe" mean to you?

The problem is that the "law" is insufficiently precise to allow an engineer to make that type of design decision.  Will you allow 3 interlocks to fail? 4? 5? 6?

Do you design a $100,000 Pinto that's absolutely safe and too expensive for your "general public" to buy?

It's nice to think that engineering is clear cut, but it's not.  You have a certain price range that you KNOW your customer is willing to pay.  You then fit all the required features into the design and find that it's double the price and you still haven't gotten it perfectly safe.

Perfect safety is a myth and to buy into that notion and ultimately deny your customers a useful product because you want to design for the 10th sigma is a disservices to the public.

The bottom line is that the public makes and allows some level of risk and couples that with a firm belief that it won't happen to them.  Otherwise, you'd never get out of bed.

Don't want to start a flame war, but consider that MILLIONS of Americans still smoke, even though the occurence and mortality rate from cancer is absurdly high.  Clearly, the smoking public makes a trade between cost and benefit as well.

TTFN

RE: What does "safe" mean to you?

Just a thought, you do realise that there is a safety critical system in a car that has NO redundancy, no backup, and if it fails the result will be unnerving at best, and catastrophic in many cases?

This is quite an interesting case to me, when I am thinking about system design. How do you design a practical system that quite simply cannot be allowed to fail?

Cheers

Greg Locock

RE: What does "safe" mean to you?

I see "safe" as:
1) complying with minimum design loads and criteria, as dtermined by long term observation and experience.
2) including some redundancy in the design can increase the degree of "safeness" but is often not a quantifiable change.
3) something is "safe" if it conforms to generally accepted practice which assumes a certain (again not quantifiable) amount of risk that has been determined as acceptable.
4) if I design a device and include a manual of operation, it is "safe" if operated within those boundaries.  I have communicated clearly what those boudaries are.
5) My designs are not made in a vacuum, but with input from our procurement, fabrication, installation, sales and legal departments.  Everyone contributes and has veto power.  Engineering has the last veto for anything not cosmetic.
6) If design guidelines are not available then full-scale testing is often the only way to know.
7) I'm sorry - life is risky!!

PS - I think Greg is referring to the Human Driver.

RE: What does "safe" mean to you?

Depends on the expected failures and number thereof.

If it were a purely mechanical system, you cuold certainly overdesign by what you consider to be an adequate margin.  Electronics are often dealt with through redundancy.

But, in the end, your system would neither be practical nor simple.

From a statistical perspective, the concept of "not" or "impossible" is anathema.  Consider the humble bolt.  How would you keep in from failing and under what set of conditions?  You'd probably wind up with a bolt that's 3 times the size and weight that you'd otherwise use.

TTFN

RE: What does "safe" mean to you?

The steering wheel, column, intermediate shaft and rack are all sub systems that have no redundancy and are safety critical.

Cheers

Greg Locock

RE: What does "safe" mean to you?

So's the driver and I'd guess that more drivers than steering columns have failed

TTFN

RE: What does "safe" mean to you?

In that case, your back up system is the seatbelt and airbags.

Edward L. Klein
Pipe Stress Engineer
Houston, Texas

All opinions expressed here are my own and not my company's.

RE: What does "safe" mean to you?

Safe is to me

FIT FOR PURPOSE

RE: What does "safe" mean to you?

That seems to be more indirection, since now we need to know what "fit" means and by how much.

The original Shuttle SRBs would be "fit" for their purpose of launching the Shuttle, but they were clearly unsafe in certain conditions.

TTFN

RE: What does "safe" mean to you?

How safe is safe?  How red is red? Obviously something one cannot specifically define in any legal document or engineering guideline.  What I accept as safe (say driving 90 on the interstate) may be perceived as horrifyingly risky to another.  And that person's perception can and does change with the situation.  You might be very accepting of my driving 90 if I am taking you to the hospital.  This is a subject that keeps lawyers occupied every day.  An engineer designs something, it's used in an unanticipated way, or in a way that, at least to others, seems to go against common sense, and something bad happens.  Along comes a lawyer and bingo!  Lawsuit and another long winded debate on the "standard of care" that should be employed by engineers.  Unfortunately, nothing of lasting value (except maybe for the attorney and plaintiff) is accomplished with all of this.  Problem is that you can't define it.  You have to rely on professional judgement and that is always subject to question by others.  It's a never ending circle.  

Don't get me wrong, I beleive that we need product liability laws etc. to protect the general public because our profession does have it's bad apples.  But, when we see hair dryers with the instruction "Do not use while asleep", or "Do not use in the bathtub or shower" don't you just wonder a bit if we are not somehow short circuiting evolution?  The woman who spilt hot coffee on her lap while going through the drive through and then sued McDonalds, her lawyer and the judge who let such a judgement out the door, absolved us from having to be responsible for own unwise actions.  They and others  opened a Pandora's box that we will never get closed.  Common sense has escaped us and will not be easily regained.  The points made here about over designing and redundancy are good ones.  However, do any of us think that such measures can protect us from lawsuits in today's world?  I remember in college hearing a professor say "the problem with trying to make something fool-proof is that the world is always busy inventing a better fool".  Good words to live by on this issue I think.  To my mind, the real problem is that Americans, as appears to be our nature, have taken a good concept and pursued it to the bitter end.  Will we ever learn?  

RE: What does "safe" mean to you?

But, I think that's why there should be a Hell for designers who design soap dispensers in bathrooms that are unusable.

Common sense, likewise, should be applied to designers and suppliers.  Up until recently, most cars did not have cupholders as a built-in feature.  When I was in college and driving home on Coke and No-Doze, I didn't have a cup holder and holding the can between my legs was a normal occurrence.  Even ignoring that aspect, a car is a moving vehicle, subject to sudden or unintended movements, and allowances should be made for a higher probability of spillage.  Even ignoring that aspect, it was shown that the McDonald's coffee was kept at so high a temperature than even a normal spillage would have potentially caused severe burns.  

McDonalds was clearly negligent in providing coffee that did not need to be that hot, particularly in the drive-through.  

The jury award is a separate issue.

TTFN

RE: What does "safe" mean to you?

Anyone that drives 90 mph on the interstate is equally as stupid as a person the uses a blow dryer in the bathtub.

RE: What does "safe" mean to you?

There must be a whole lot of stupid people in Atlanta, then.  A few years ago, a traffic study was done on the loop around town, and the AVERAGE rush hour speed was 85 mph.
  In good, dry conditions, with light traffic, in a sound vehicle, 90 mph on an interstate is less dangerous than 35 mph.

RE: What does "safe" mean to you?

Well for me in the UK oil & gas industry, under the goal setting safety regime imposed after the Piper disaster, the definition of "SAFE" is "As low as resonably practicable" (ALARP).  This means that when you would have to spend more to make something safer than the cost of the risk of the event, it is ALARP.

Risk is defined as the probability of an event multiplied by the consequences of that event, so something that will happen once a century but kill loads of people is the same risk as soemthing that happens daily and causes a minor injury each time, and both must be dealt with.

So, for the Safety Cases I compile before each well we drill, we'll look at all the things that could go wrong and then do a cost benefit anaylsis: we calculate the likelyhood of an event and the consequences of that event (using a number of criteria: material damage, damage to reputation, environmental damage and value of loss of life & limb using actuarial tables).  Then we work out he cost of reduing those risks.  Usually it's just a matter of emphasising something in the procedures or changing how we're going to do something, but for example, I have proposed to the UK authorities ommitting a downhole safety valve on a certain type of well as the risk of a blowout was smaller than the cost of installing and maintaining that valve, and the proposal was accepted.  

The problem the general public have with this approach is two fold:
1.  they don't like the idea of there being any risk at all.  They perceive this approach as "well only one person per year will die so it's ok".
2. The public gernally underestimate risk in situations they are used to (crossing the road, or driving in their cars for eaxmple) but overestimate the risk in situations they are unaccustomed to (flying....)

The SAfety Case system is gernally 'better' than the regulations type safety system, as it forces teh designer to think about what they are designing rather than simply looking up a regulation and making sure they've ticked the box.  Sadly, like most improvements in safety engineering, the goal setting system is usually only adopted after a disaster: Piper Alpha in the UK, the Alexander Kielland in Norway and the Ocean Ranger in Canada....

RE: What does "safe" mean to you?

ALARP would have said that the Ford decision in the Pinto fuel tank case was correct.

The calculation went wrong when the punitive damages were set so high, precisely BECAUSE a cost benefit calculation had been used!

Cheers

Greg Locock

RE: What does "safe" mean to you?

greg- not being an automotive engineer (Hell, I can hardly drive according to my wife!) I can't comment on the Pinto fiasco.  But I'd have thought that with the design as it was, the probability of a major accident & fire would have made the risk unacceptible even if the cost of each accident and fire had been low?

Also, we use other criteria beyond simple finacial cost to mearsure the effects of risk when doing our risk assessment- loss of reputation for example.

RE: What does "safe" mean to you?

I know that this is an old thread, but...

The case of the Pinto is an interesting one.  

Quote (GregLocock):

ALARP would have said that the Ford decision in the Pinto fuel tank case was correct.

The Pinto cost benefit analysis had two main flaws:
(a) It was woefully inadequate, and
(b) The assumptions were badly wrong.

Cost benefit analysis is a useful tool for determining acceptable risk, but it is precisely that.  As with most tools, the quality of the output is directly related to the quality of the input. As drillernic points out, it is just one tool.  There are other risk assessments that could and should have applied in this case, not least common sense.
In what sense is addition of a part costing a few dollars not practical?

If there was any justification for that decision whatsoever, it would be that we have to take into account the context and date of that decision.  However, times have moved on.  Product recalls happen on a wide range of products, and safety is very much of the forefront of most (I would hope all) engineer's minds.  Such analyses are now relatively commonplace for assessing risks in a wide variety of applications.  I hope that it's not being seriously suggested that the same conclusion on the Pinto would be reached today.

RE: What does "safe" mean to you?

Oh, where was it inadequate?

Number of crashes * damages per crash vs number of cars sold * cost per car of fixes

only has four variables.

As I said, my understanding is that the "damages per crash" estimate was wrong, and the reason it was wrong was that the juries were annoyed/horrified that anybody could be so cold blooded. The actual figures are pretty revealing. In practice 27 people died, and 2 million vehicles were sold before the changes were introduced. At the usual 2004 rate of 4 million $ per person, that's about $54 per vehicle in current $. The cost save was $11 in 1974 dollars, which sounds about right.

According to this presentation

www.nottingham.ac.uk/scheme/admissions/ currentstudents/Lecture%207%20-%20Economics.ppt

the actual calculation used 180 deaths+180 serious injuries +2100 cars, at $200000 $67000 and $700 respectively, and sales of 12.5 million vehicles, with a fix cost of $11 each.

So, as I said, the error was in the punitive damages, because of the cover-up, not the analysis. Where do you disagree?

Yet, oddly, this type of calculation is used all the time. Incidentally, do you buy the exact same tyre for your car that it originally had? and do you always specify the top of the range safety features when you buy your car? If not, you have just made a cost benefit decision, with, I would argue, even less information.

http://walterolson.com/articles/gmtrucks.html for a non hysterical account.

Cheers

Greg Locock

RE: What does "safe" mean to you?

Having had a bit of a dig around, I strongly suspect the memo and calculation quoted above in the Nottingham presentation were NOT what was used to justify the original Pinto decision, they were a response to a later proposal to introduce better rollover protection. The actual memo from which that calculation is made is available on-line, it is several pages of reasonably well written stuff.

I haven't got the inclination to research further, the lawyer in the newspaper article is probably a good jumping off point for further research.

Cheers

Greg Locock

RE: What does "safe" mean to you?

It depends on which figure you believe on the fatility rate.  Doing a quick estimate, it would appear that 27 fatalities over 5 years falls in around the 'Tolerable' region - i.e. should do something if not excessively expensive - on the ALARP scale.  180 - 900 fatalities per 5 years falls into the unacceptable region - i.e. must do something regardless of cost.

I am not sure that I believe either the 27 nor the 900, but suspect the truth is somewhere in between.  I tend to believe neither journalists nor lawyers, when it comes to 'facts', but that's another thread.

My comment on the inadequacy comes not from the complexity of the calculation, but rather that it appears to have been taken in isolation from anything else.

I do agree that there is a difference in the general public's perception of risk between 5 fatalities per year from 2 million units, and a risk of 1 fatality per 400,000 years from 1 unit.  A cost of $11 per unit in one to reduce the risk, equates to a cost of $22million per unit in the other.  The vast majority of people would pay $11 to save their (or a loved one's) life, few could afford $22million.  Whether you would pay $11 to save a totally unknown person's life would be down to the ethics of the individual.  Some will pay $11, some $1, some $111, while others will pay nothing at all.  When you see the effects of failure to pay the $11, that person becomes (apparently) known, and this will sway many people, but if it's hidden - who knows?  (Incidentally, that's why so many people chose to vote for political parties who promise to cut taxes - they don't necessarily see the effect of that policy.)

RE: What does "safe" mean to you?

Safety first in construction or structural engineering means to prevent loss of life and injuries.  How much level of risk can the engineer may take is not really dictated by engineers but has already been established by minimum criteria in building codes.

I'm sure similar criteria exist for consumer products.

RE: What does "safe" mean to you?

Here's a situation.  When football started, no-one wore helmets - like Rugby today.  Then people started to get tired of having broken noses; they started wearing them.  The trend has continued.  Now we have suits against football helmet makers for something that I am not sure if it is even mandatory to wear!  Risks are part of the game; it is part of life.  I think, in many instances, we go far too overboard in applying a concept of "risk-free".  It doesn't exist.  This is not to say we should make risky products or provide risky designs.  But we cannot design things for 100% freedom from risk.  It is not the maker's problem if the user mis-uses the product - and I don't mean inadvertantly  - but in a grossly stupid way.  It is time we get back to reality.

RE: What does "safe" mean to you?

As with anti-lock brakes, the safety equipment allows the level of violence and danger to increase well above what might have been the case without the equipment in the first place.

Can you imagine being tackled by a 300-lb lineman running at full bore without padding and living to talk about it?

The issue is that once the equipment is sold as protection, it should do its job.  If it doesn't, the manufacturer should be liable.

TTFN

RE: What does "safe" mean to you?

Trevor A. Kletz in his Critical Aspects of Safety and Loss Prevention (Butterworths) brings interesting observations on the subject. I recommend reading this book of his.

RE: What does "safe" mean to you?

GREG: Re: Shuttle Columbia. They did do a failure mode analysis that involved using an air cannon to fire chunks of foam at the leading edge of wing sections. The result? Everyone gasped as the foam punched a huge hole through wing section 8 under conditions that were like those at launch when the anomaly occurred.

Regards


Andy

RE: What does "safe" mean to you?

Firing a cannon is not an analysis.

As with many systems, particularly, the Shuttle, bad practices that result in no immediate ill effects wind up becoming the norm.

Lest you think that you are immune from that, I'll remind everyone that there are those that seriously think that they can drive as well as anyone after a night of heavy drinking.  There are those who think nothing of driving at 100 mph down the freeway or even down a large street.

TTFN

RE: What does "safe" mean to you?

Firing a cannon is not an analysis- it is a test to provide data for correlation against an analysis.
It could also show that analysis was needed in another area entirely!

Jay Maechtlen

RE: What does "safe" mean to you?

Loss prevention and risk management are two more recent disciplines added to safety in the chemical industry, complementing and expanding it.

Nowadays safety has become almost as important as production, and the various attached complex theories (models, mathematical techniques, etc.), and applied practices, have transformed it into a real scientific field of study.

It is now a discipline capable to anticipate and identify hazards and quantify risks, in order to enable taking decisions and steps towards forestalling accidents and their consequent damage in its various forms.

Could that be considered a reasonable definition ?

RE: What does "safe" mean to you?

In scanning this thread I may have missed it, but in case it wasn't mentioned, here's a link to US DoD standards, handbooks, and specifications, including MIL-STD-882 "System Safety", which defines safety in terms of both probability of occurrence and severity of consequences of occurence. There are various analysis techniques (preliminary hazard analysis, fault tree analysis, event tree analysis, failure modes and effects analysis) that can be used to identify and quantify this for a given design or process. Then mitigating measures can be applied to reduce the assessed risk within given constraints.

http://assist.daps.dla.mil/quicksearch/

Good luck,

-MC

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources