I was just reading posts on F2000.com and came across a lively string on the new seat belt rules and the Sports Car article. This is from Iain Walker.
Well, just to add to this discussion from the POV of someone who does durability
testing - here is a copy of a letter I sent to Ken Brown today (warning LONG post). It
includes most of the issues already covered in this discussion.
-Iain
I read the article on seatbelt durability with great interest in the latest SportsCar
magazine. I am a research scientist with a background in mechanical engineering and
one of my jobs is to perform durability testing (of duct tape yes really!). I was
hoping to learn something constructive about the issue, but instead the article raised
more questions than it answered, and left SCCA members to make ill-informed
decisions. As you can see from my following points, I found the technical aspects of the
article to be highly questionable, and the implications to be completely misleading.
To determine if SCCA needs to do anything about fixing a problem, we should first know
if there is a problem to fix. In this case, SCCA should publish data on the number of
seatbelt failures over say, the last five years so that SCCA members can make an
informed choice; as you say in the article each member must assess his or her safety
issue relative to restraint systems. We should run a sweepstakes Ill wager no-one
has been seriously injured due to belt failure (by which I mean the belt material itself
not incorrect installation or use). Ill also wager that SCCA members know this too and
that is why this article brings the SCCA Technical Department into disrepute because
the assertions in this article just dont match-up with peoples life experience. I know
that risk analysis means that you cant take this approach we expect injuries to be
rare events so personal anecdotes have little value. But you should try to be realistic in
the risk analysis so that SCCA members will not just dismiss articles such as the one we
are discussing. This is important there is a great deal of implied trust between the
SCCA Technical Department and the general membership who rely on them to make
good technical decisions to make racing safe. Some SCCA members (particularly
engineers who understand about testing, interpreting test results, mechanical
performance of systems, standardized testing (including accelerated testing), etc.) are
pretty scathing about the technical abilities of SCCA after reading this article including
me.
The article did not show an understanding of the nature of the accelerated testing
results that were presented. The exposures used in FL and NV are industry standards
for extreme or accelerated testing. All the companies and laboratories performing these
tests are adamant that results from these types of tests in no way resemble expected
lifetimes they are used as a guide to comparative performance. Even if the two years of
exposure is taken directly, most SCCA cars are only exposed for few hours per year, so
the life of the belts could be inferred from the data presented in the article to be on the
order of greater than 20 years. In addition, the test procedure for these products
needs to include the FIA seat belt test method in order to determine their ability to
protect the wearer in the circumstances close to those in which they will be used.
To bring up warranty issues is disingenuous. We expect products to last beyond the
minimum warranty period. A warranty is just that for minimum life, not typical life, and
they are created to protect manufacturers from long term liability, not users or
consumers of products.
If belt weakness is such a big problem, why havent we heard about it? And why
havent lawyers exploited this problem for the benefit of their clients? Millions of
passenger cars rely on much weaker belts than in a racecar and we dont hear about
them breaking all the time. The auto industry is an incredibly conservative and risk
averse business if this was an issue you can bet they would be using different
materials or making seat-belt replacement part of routine maintenance. Do you have
any explanation for why racecars that spend only a few hours a year in sunshine are
much more at risk than a passenger car?
The differences between FIA and SFI testing were interesting. The FIA test is a fairly
realistic situation for seatbelt use sudden short term loading. The SFI test is implied
by the article to be at a steady load. This might be OK for tow ropes but is completely
inappropriate for seatbelts. We need to investigate the difference in performance when
web belts are dynamically loaded and statically loaded. I suspect that (like many man
made materials) they are sensitive to rate of leading as well as total load. For example,
they will exhibit hysteresis in cyclic loading and they will creep under steady load.
Another thing to think about is that the mandated replacement after two years means
that there will be many more removal and installations of seatbelts increasing the
chances of incorrect installation and the resulting dangers. This needs to be included in
the balance of safety issues. It is highly likely (given that most seatbelt failures are due
to incorrect installation and use, and we dont have any recorded incidences of material
failure) that mandated replacement at shorter intervals will reduce safety. This is simply
unacceptable.
In summary, it would be a great disservice to the membership of SCCA if this were to
lead to mandated short lives for seatbelts. However; it would be interesting to perform
scientifically valid tests on seatbelts. The results of this testing could then be made
available to SCCA members who could then use their own judgment about reducing
replacement intervals if their racecars are constantly exposed to the elements, for
example.
Additional information (from a brief internet search):
I am an expert in durability of duct sealants, if you want more specific expert opinion on
seatbelt materials, how about reading these publications:
www.atlas-mts.com/client/...ions.shtml
www.addall.com/Browse/Det...28568.html
And what about other applications. For aircraft 10 year lifetimes are used:
www.casa.gov.au/avreg/air...25/002.htm
Belt material failure is not in the list of seat belt failures cited by analysts:
www.safetyforum.com/seatbelts/
or lawyers:
www.seatbeltdefects.com/s...efault.htm
Well, just to add to this discussion from the POV of someone who does durability
testing - here is a copy of a letter I sent to Ken Brown today (warning LONG post). It
includes most of the issues already covered in this discussion.
-Iain
I read the article on seatbelt durability with great interest in the latest SportsCar
magazine. I am a research scientist with a background in mechanical engineering and
one of my jobs is to perform durability testing (of duct tape yes really!). I was
hoping to learn something constructive about the issue, but instead the article raised
more questions than it answered, and left SCCA members to make ill-informed
decisions. As you can see from my following points, I found the technical aspects of the
article to be highly questionable, and the implications to be completely misleading.
To determine if SCCA needs to do anything about fixing a problem, we should first know
if there is a problem to fix. In this case, SCCA should publish data on the number of
seatbelt failures over say, the last five years so that SCCA members can make an
informed choice; as you say in the article each member must assess his or her safety
issue relative to restraint systems. We should run a sweepstakes Ill wager no-one
has been seriously injured due to belt failure (by which I mean the belt material itself
not incorrect installation or use). Ill also wager that SCCA members know this too and
that is why this article brings the SCCA Technical Department into disrepute because
the assertions in this article just dont match-up with peoples life experience. I know
that risk analysis means that you cant take this approach we expect injuries to be
rare events so personal anecdotes have little value. But you should try to be realistic in
the risk analysis so that SCCA members will not just dismiss articles such as the one we
are discussing. This is important there is a great deal of implied trust between the
SCCA Technical Department and the general membership who rely on them to make
good technical decisions to make racing safe. Some SCCA members (particularly
engineers who understand about testing, interpreting test results, mechanical
performance of systems, standardized testing (including accelerated testing), etc.) are
pretty scathing about the technical abilities of SCCA after reading this article including
me.
The article did not show an understanding of the nature of the accelerated testing
results that were presented. The exposures used in FL and NV are industry standards
for extreme or accelerated testing. All the companies and laboratories performing these
tests are adamant that results from these types of tests in no way resemble expected
lifetimes they are used as a guide to comparative performance. Even if the two years of
exposure is taken directly, most SCCA cars are only exposed for few hours per year, so
the life of the belts could be inferred from the data presented in the article to be on the
order of greater than 20 years. In addition, the test procedure for these products
needs to include the FIA seat belt test method in order to determine their ability to
protect the wearer in the circumstances close to those in which they will be used.
To bring up warranty issues is disingenuous. We expect products to last beyond the
minimum warranty period. A warranty is just that for minimum life, not typical life, and
they are created to protect manufacturers from long term liability, not users or
consumers of products.
If belt weakness is such a big problem, why havent we heard about it? And why
havent lawyers exploited this problem for the benefit of their clients? Millions of
passenger cars rely on much weaker belts than in a racecar and we dont hear about
them breaking all the time. The auto industry is an incredibly conservative and risk
averse business if this was an issue you can bet they would be using different
materials or making seat-belt replacement part of routine maintenance. Do you have
any explanation for why racecars that spend only a few hours a year in sunshine are
much more at risk than a passenger car?
The differences between FIA and SFI testing were interesting. The FIA test is a fairly
realistic situation for seatbelt use sudden short term loading. The SFI test is implied
by the article to be at a steady load. This might be OK for tow ropes but is completely
inappropriate for seatbelts. We need to investigate the difference in performance when
web belts are dynamically loaded and statically loaded. I suspect that (like many man
made materials) they are sensitive to rate of leading as well as total load. For example,
they will exhibit hysteresis in cyclic loading and they will creep under steady load.
Another thing to think about is that the mandated replacement after two years means
that there will be many more removal and installations of seatbelts increasing the
chances of incorrect installation and the resulting dangers. This needs to be included in
the balance of safety issues. It is highly likely (given that most seatbelt failures are due
to incorrect installation and use, and we dont have any recorded incidences of material
failure) that mandated replacement at shorter intervals will reduce safety. This is simply
unacceptable.
In summary, it would be a great disservice to the membership of SCCA if this were to
lead to mandated short lives for seatbelts. However; it would be interesting to perform
scientifically valid tests on seatbelts. The results of this testing could then be made
available to SCCA members who could then use their own judgment about reducing
replacement intervals if their racecars are constantly exposed to the elements, for
example.
Additional information (from a brief internet search):
I am an expert in durability of duct sealants, if you want more specific expert opinion on
seatbelt materials, how about reading these publications:
www.atlas-mts.com/client/...ions.shtml
www.addall.com/Browse/Det...28568.html
And what about other applications. For aircraft 10 year lifetimes are used:
www.casa.gov.au/avreg/air...25/002.htm
Belt material failure is not in the list of seat belt failures cited by analysts:
www.safetyforum.com/seatbelts/
or lawyers:
www.seatbeltdefects.com/s...efault.htm

















