i had an interesting discussion over email about a year ago which dealt with the issue of helmet foam padding vs. suspension system and this might provide insight (bear in mind that it's one person's personal opinion) into to why the USMC was skeptical of a foam system. i've cut and pasted some of it here (some extraneous stuff is edited out). It's long, so ignore it if you're not interested:
XXX: "Dear Sir,
First, congratulations on an excellent website.
I wanted to point out a few issues related to foam padding added to combat helmets.
USMC is looking at the foam-pad products you've reviewed on your website; however, neither product has passed testing for attenuation of ballistic energies applied to the helmet shell. Protection against impact from a fall is very different from the very short-duration high-energy impact from a bullet or fragment striking the shell.
Our current concerns are that the pads absorb moisture from perspiration, increasing the transmission of ballistic energy, and the material hardens in cold temperatures, also increasing transmission of ballistic energy. These factors may allow sufficient transmission of energy to the brain to negate the helmets protective benefits.
For comfort alone, they are an improvement, but to prevent traumatic brain injury, they may actually increase the likelihood. Until manufacturer testing demonstrates adequate protection, I am skeptical.
This information is unofficial and not for attribution and does not represent official Marine Corps policy or opinion. However, it is the basis for current USMC hesitance to adopt these helmet suspension systems.
I thought this information might be of interest to you and your readers.
RS
CDR XXX (edited for PERSEC), MD, MPH
Preventive Medicine Officer
Headquarters, U.S. Marine Corps
address XXX"
MM: hi XXX,
thanks for writing and the kind words on my site. thank you also for
sharing some insight into the issue.
i was speaking to the crye precision guys about precisely the same
thing - they were talking about blunt trauma vs ballistic protection
requirements.
i have a few questions, so do humour me, as i'm quite ignorant on the
subject.
how has the skydex vs oregon areo pad performed under the conditions
you listed? the skydex system relies on geometry, and from what i
understand, is a closed system, and is unable to absorb much moisture.
how much moisture does the oregon aero pad absorb, also being closed
cell?
in cold temperatures, what is the temperature of the foam when worn in
a head? body heat coming off the head is going to warm the foam
padding to a certain extent - does the cold-temp testing take body
heat into account or is testing done on a non-heated test fixture?
By the way, do you mind if i share or discuss the information we're discussing with others?"
XXX:"Agree on the head heating the padding. But we test for worst case
situations. Helmet off head until the last moment so no time to heat up the
pads.
Old pads with worn surface allowing fluid penetration? Prolonged wear in
tropical climates so lots of slow soaking over days without time to dry out,
etc.
Dunk the helmet and repeatedly squeeze the pads while submerged. Sure it's
tough, but daily wear in a combat environment is tough.
Bottom line, distance is the only consistent protective measure for a bullet
(or fragment) hitting a helmet. Look at all the combat helmet designs over
the decades. They use a suspension system that allows free flow of air
around the head and provides a gap between the shell and the head.
Engineers figured it out a long time ago but we seem to be forgetting it
now.
To answer your question, no helmet pad vendor has provided test results for
ballistic protection under the conditions noted.
Share away. Just make sure they understand that this is a personal, and not
official Marine Corps, inquiry."
MM:"i understand about testing the worst-case scenario. possible vs
probable. you've got me thinking - on the cold-heat issue, i was
wondering how long it takes for the head to warm the pad up, which of
course, depends on ambient temperature. also, if it's that cold
outside, soldiers might wear a fleece helmet liner that might slow the
transfer of heat from the head to the pads and helmet.
i stuck both dry pads in the freezer for a bit. the oregon aero
pad did harden up slightly, whereas the skydex one didn't noticeably.
they both returned to room temperature within half a minute of being
held in my hand.
i think i understand what you're getting at, though. if pad material
is wet or cold enough to harden, a short-duration impluse to the shell
of the helmet can be transmitted through the pad almost as if it were
solid, as the duration of the impact is too short for the pad material
to compress.
now, aren't the oregon aero pads used in the ACH/MICH? i'm assuming
that the MICH was tested using those (or identical) pads under all the
conditions we're talking about here. how did the MICH pad system get
adopted if it didn't perform under ballistic tests?"
XXX:"My concern is ballistic impacts from
bullets/fragments striking the helmet.
I'd be interested in knowing whether closed cell foam absorbs or transmits
energy delivered by a 9mm bullet striking the shell.
Key point, it's all about objective certified testing. The pads MAY be OK,
but it has to be proven in the ballistic environment, not just in drop
testing. When marketing efforts exceed testing efforts bad things can
happen and there may be unintended consequences.
For the Marine Corps, the official helmet liner is the hammock-type liner.
There are a lot of the pad systems in use in theater, but they aren't
officially sanctioned. I have no idea about Army's system."
MM:"i did a bit of looking on the OA website
(
http://www.oregonaero.com/p81BLSS1_01.html), and it says that the pad
is enclosed in a coating that provides the waterproofing. that's why
it wasn't able to absorb any water, but now you've got me thinking
about the coating wear and puncture - would the foam still not absorb
moisture, or would it?
another thing they stated was "The BLSS™ Kit has already passed
testing for submersion to 66' in salt water, exposure to fuels, oils,
insect repellants, camouflage face paint and gas mask use. It also has
passed temperature test of –40˚F to +160˚ F and ballistic testing. "
so, they do claim to have done ballistic testing on it - what testing
was done they don't specify.
it's very surprising to me (and worrying) that they've been fielded if
they haven't passed ballistic testing (either independantly or by the
military).
another issue that i'm wondering about is backface deformation of the
shell - standoff distance with air space seems to be the best way to
protect the user from that. is that another concern you have with
pads?"
XXX:"In reading the fine print of their "ballistic testing" they used ANSI
standards for construction hard hats and an impact velocity of 3m/s.
Their velocity is off by a factor of, oh, let's just say 100. 300 m/s for a
slow 9mm round.
Standoff is used by every other combat helmet to protect the skull. When
you fill that space with anything that could transmit the energy, you have a
potential for a problem.
Since Oregon Aero hasn't tested for this, they can't really say that this is
a safe system for a combat helmet. A crash helmet, sure, but not for
combat.
That's the take home point. For police where trips and falls are most
likely, it's fine. If they expect to survive a bullet/fragment hit, maybe
not.
And BTW, the ANSI standard Oregon Aero used is for testing is for
recreational helmets like bicycle and motorcycle helmets. Not an appropriate
standard for a combat helmet."
MM:"quick question back at ya (playing devil's advocate) - have you heard
any feedback concerning the issues that we're discussing pertaining to
injuries to soldiers whose ACH/MICH have been hit by rounds, that show
that the current pad system can (in some cases), protect the wearer
less than a conventional suspension system?
i've seen some reports on MICH's getting hit by rounds or IED
fragments, and i recall the most serious injuries mentioned being mild
concussions.
much of the feedback i've seen is comfort/weight related, not
ballistic performance."
XXX:"A Marine who is impaired due to a mild concussion is at increased risk of
more serious injury in a high-threat environment. You can't just "knock it
off" because you're disoriented. So even a mild concussion is a concern if
it could be avoided entirely.
That's why we do testing because in the real world you can't control for the
variables. Any idea of the impact velocity or size of the fragments that
caused the mild concussions? We have no way of predicting performance when
we don't really know whether there should or shouldn't have been symptoms.
Either the helmet system did really well (exceeded standards) or very poorly
(failed standards), but we don't know without testing to standards.
Same reason we crash test cars in a lab. It's not real world, but it is
reproducible, comparable and applicable."
MM:"understood. i didn't think about the ability to continue on with the fight.
i completely agree with you that anything approved for use should be
certified/tested according to some standard, be it NIJ ballistic
helmet certification or some mil-std. at least we know that it meets
minimum requirements. or hope so."
I contacted both oregon aero and skydex and asked them about ballistic testing of their pads:
"i'm asking about the ballistic testing as some people have asked me
about it, and i didn't have the information in order to answer them.
the question was brought up as a concern about a pad system vs. a
conventional suspension system (that uses standoff distance to isolate
the head from the shell).
some of the issues brought up are:
1. when subjected to a bullet hit, which is a very quick impulse, does
the foam have time to compress enough to absorb the shock and how much
of it is transmitted to the head.
2. the foam hardens in cold temperatures and takes a while to warm up
after being worn. it might not be likely that someone puts a cold
helmet on with stiff foam and then gets shot, but they always look at
worst-case scenarios.
3. is the OA foam closed cell, and can it absorb water/sweat if the
outer coating on the pad gets punctured or wears. the question here is
shock transmission through a liquid medium vs air space.
safety systems (SSC) sent me their version of their pad kit, which
uses skydex, as opposed to foam, like yours. the same issues apply,
and i've asked them for information as well. i did a dunk test in
water (soaked the pads and tried to squeeze them like sponges). your
pad wouldn't take on any water, but i didn't want to sacrifice a pad
and puncture it or cut a hole in it to see if that would affect it.
theirs uses a two-layer system - skydex (more rigid) and an open cell
material (more spongy). the open cell material held water.
i then stuck them both in the fridge for a while. your pad became
stiffer, and the open cell material on the SSC stayed pretty much the
same.
i asked SSC the same questions i emailed you with, and they're sending
me some test data. however, they said that there is NO requirement for
the suspension/pad system to be tested during the shell's ballistic
tests. the shell is tested and passed for it's ability to stop
bullets. the suspension system usually undergoes shock absorption
testing for blunt trauma/low impulse impacts, but isn't tested to see
how much shock is attenuated during a ballistic hit. at least theirs
was not tested that way.
the concern was that even though the soldier's life is saved, the
ability to continue fighting might be impaired for a brief period
(from mild concussion etc) and can further endanger the soldier. it's
a valid point.
i wasn't aware that the helmets aren't tested that way (i might be
wrong, which is why i'm asking you), and i'm wondering what
requirements the Army has and if the ACH/MICH pads system went through
ballistic shock testing before it was adopted."
Answer from skydex:
"The ACH helmet specification does not require the pad sets to meet any
impact requirements during ballistic impacts, only NON-ballistic impacts.
For ballistics, the spec has a lot of requirements for "ballistic
resistance", i.e. - will the shell stop the bullets. The pad sets, or
suspension system as the spec calls them, are somewhat independent of
ballistic resistance of the shell and there are no requirements that the
pads have to meet during the ballistic resistance testing."
OA pretty much answered along the same lines - the testing they perform is for blunt trauma, not ballistic shock (as of the time of this correspondence). i played phone tag with the owner of OA but never got a chance to discuss the other details.
MM to XXX:"i just got of the
phone with the skydex guy (who make the pads for safety systems), and
he said that they have tested their pads according to the Army ACH
spec.
he agrees with the issues we brought up, but until a spec requires
ballistic shock testing, they haven't looked into going beyond the
current requirements.
the OA system has been approved for use in the MICH by the Army, the
safety systems one hasn't yet.
i think the problem is that the manufacturers are not required to test
ballistic shock - if the Army or USMC puts forth a requirement to test
to some kind of standard, the manufacturers will have to meet that
criteria. but until then, i don't think we're going to see anything
along those lines.
i've attached a copy of the Army ACH helmet performance spec, which
covers the shell and the pads."
The end result of the correspondance was that the issue was (is) still open, as far as i know. i didn't investigate further.
cheers,
MM