From: Andrew Johnson <ajohnson@augean.eleceng.adelaide.edu.au>
Subject: Re: Change of M17A2 mask to M40 mask?
Summary: its ergonimically superior
Organization: Electrical & Electronic Eng., The University of Adelaide
Date: Wed, 18 Nov 1992 14:50:33 GMT


From Andrew Johnson <ajohnson@augean.eleceng.adelaide.edu.au>

Don Palmrose writes:
>
>Dion VanAtter writes:
>>
[ stuff about M40 filter being an obstuction deleted ]
>>
>
>It is because in the M17A2 one cannot rapidly change the filter.  In a CBR
>(chemical, biological, and radiation) environment, your filter must be
>periodically changed because its effectiveness goes to zero after 3 or 4 hours.

Or less, only about 30 min if they are using nerve agents.  :-(

>With the new M40 mask, the user can quickly replace the filter and there is
>an internal valving so one does not breath in the bad air while performing the
>switch.  Also the full visor face shield allows for much greater vissiblity
>(sp?) and may allow the user to still wear a more normal set of glasses.
>
Having worn both I'd just like to say that the M40 ( Mark 11 I think - itsi
British originally ) is infinitely superior to the M17. Everyone I know who
has thinks the same. After a couple of km running in an M17 with the suit on,
you can hardly see out of the bloody mask at all, and breathing is very
restricted ( as Don no doubt knows ). To change the filters, which you have
to do regularly if you want to stay alive, you have to remove the mask,
which is a very useful design feature ... NOT. And drinking with an M40 is
much easier. And it doesn't fog up as much. And your field of vision is better.

>When I was on active duty in the US Navy, I was virtually blind when wearing
>the M17A2 since I could not get a pair of glasses that would work with the
>mask.  If there were a special pair of glasses, supply could not find or
>order them.  What I had to do was place my glasses over the outside of the
>mask.  Needless to say, one looks like the nerd from outerspace when wearing
>the glasses like that ;-)
>
We were assured that there is a special version of the M17 mask that has an
attachment for special glasses which sort of clip in around the nose.  You
can't wear any sort of conventional glasses with it without breaking the seal
around the face. Lucky I don't need to wearn mine much.

>
>In summary, what you loose in freedom of movement you gain in orders of
>magnitude in ease of operation and in long term endurance.
>
Spot on. The loss in freedom of movement isn't much really. IE I never noticed.
Mind you, the longest I've had to wear one for at a stint is about 3-4 hours.
The fatigue of troops wearing M40s is at a lower rate than those wearing M17s,
and this is what CBW is really about - increasing the fatigue rate and lowering
the efficiency of your opponents, and imposing another logistics strain on them.
Surprise use of CBW in a major conflict ( ie surprise in the sense that the
use was not anticipated and CBW gear not issued to troops ) is very unlikely,
and hence is unlikely to inflict large scale casualties, beyond the initial area
of their use - because by then everyone else will be in their suits and closing
down their armour. It fine for wiping out civilians in their millions though. If
you use it against a well disciplined and trained army mostly what you do is
slow them up. And of course - you know you are going to go chemical, so your
bodies are already in their suits as the MICVs roll over the LD in the assault,
and the nerve gas shells rain down on the enemy position as you near smallarms
range ... its tactically advantageous. But AFTER that they are going to ASSUME
you will use CBW EVERY time, and take action accordingly.

So having a mask that is more comfortable to wear for extended periods,
has a less restricted field of vision and can have the filters easily changed
whilst maintaining integrity of the suit is a strategic advantage.

All of the above IMHO , of course ...

-- 
Andrew
ajohnson@eleceng.adelaide.edu.au

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