UFC 4-211-02N
10 January 2005
including change 3, 13 April 2007
\ CHAPTER 4 PLASTIC MEDIA BLAST HANGAR
4-1
FUNCTION.
Design the plastic media blast (PMB) hangar for use only as a part of a NADEP
or a selected intermediate maintenance activity as determined by the major
claimant and approved by the Shore Development Board for cleaning, painting,
and curing aircraft surfaces using production line methods. Provide work-bays,
storage, and administrative spaces.
4-1.1
PMB Material.
Data sheets for the Plastic Media blast (PMB) material indicate it is non-
combustible at the particle size that the material will be initially used at (a PG-1
size which is 5% > 12 mesh, 12 mesh > 80% > 16 mesh and 16 mesh > 15% >
20 mesh). It is typical for many dusts that they are not combustible until they
reach a particle size of 420 microns or less in diameter (i.e., material passing
through a U.S. No. 40 Standard Sieve). The PMB material behaves in this
manner, being combustible when particles are small enough; and thereby having
the potential to generate a dust explosion when enough of these very small
particles are in a uniform fine suspension in air and are heated to a high enough
temperature.
4-1.2
PMB Recycling.
In the PMB process for aircraft stripping functions the blast media is recycled
when particle are between 12 and 60 mesh. As particle size becomes smaller
(i.e. pass through a 60 mesh sieve) the particles become uneconomical for the
stripping process and these smaller particles are removed in the stages one and
two of the media reclamation process. As particles between 12 and 60 mesh
are recycled, some of the media that is returned to the stripping process falls in
the particle size range that is combustible (i.e. that between 40 and 60 mesh).
4-1.3
PMB Hangar Cautions.
The premise of the building design is that the system interlocking, media
recovery, media recycling and house keeping policies in the facility shall be such
to ensure that small dust particles are not allowed to accumulate anywhere in the
hangar space. Thus the hangar bay space will not be classified a hazardous
space despite the presence of PMB material, which under some circumstances is
a combustible dust.
Designers should be aware that PMB materials in a laboratory setting have been
shown to form dust clouds that can result in dust explosions. Research reports
by US Bureau of Mines have concluded that:
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