I agree with the implied characterization of the Perry memo as short-sighted
(Secretary of Defense Perry wrote the Clinton-era memo that forced the
retirement of a lot of military standards). The idea was that the
commercial world did things a lot cheaper so the military ought to use parts
built to commercial standards. The part they missed was that the biggest
reason commercial products are cheaper is economies of scale, although we
have all heard of $600 toilet seats, etc. The philosophy today is that the
contractor must meet performance requirements, but the military should not
tell the contractor how to design to meet the (performance) requirement. In
the case of MIL-STD-454, requirement 1, the performance requirement would be
that the equipment be safe during a fault condition. It would then be up to
the contractor to demonstrate safety. In practice I would expect this
means they do design per the military standard or handbook, expect when that
becomes expensive or counterproductive and they have the freedom to try
another approach. Vis-a-vis MIL-STD-454 requirement 1, you could say that
the commercial power cord is superior to a MIL-C-38999 type power connection
because the commercial power cord has a safety ground pin that is longer
than the others, thus the ground connection is made first, and broken last.
In a MIL-C-38999 connector, all pins have the same length. A simple fix for
that using a MIL-C-38999 connector is to attach the ground wire to the
backshell, because the connector shell makes ohmic connection before the
pins on connection, and breaks ohmic connection last upon disconnection.
--
From: k3row k3...@eurobell.co.uk
To: emc-p...@majordomo.ieee.org
Subject: MIL-HDBK-454 (Safety)
List-Post: emc-pstc@listserv.ieee.org
Date: Sat, Jul 13, 2002, 2:06 PM
Over the years a number of US MIL standards have been replaced by MIL
guidance handbooks (for instance MIL-STD-454 has been replaced by
MIL-HDBK-454). The MIL standards were full of shalls whereas the
MIL-handbooks are full of shoulds. This shift is rather unfortunate from a
contractual point of view since MIL handbook 454, for instance, states that
it cannot be used to place mandatory requirements and the designer need not
comply with the guidance provided. This seems to be particularly unfortunate
since MIL-STD-454 (Requirement 1) was probably the most important souce of
MIL personnel safety requirements. The specifications for numerous US
military items, however, still refer to this guidance handbook as if it is a
repository of mandatory requirements. In reality this seems to me to leave
the issue of what the equipment design actually complies with as completely
undefined.
I would like to hear any opinions as to how MIL-HDBK 454 is perceived from a
contractual standpoint. How much freedom do US military equipment designers
out there feel they actually have, given the complete lack of shalls?
Dave Palmer, UK
