(54ca) Combustible-Dust Flash Fires:  Flame-Resistant Clothing

COMBUSTIBLE-DUST FLASH FIRES:
FLAME-RESISTANT CLOTHING

A presentation to the 14^th
Global Congress on Process Safety

April 22 to 26, 2018

at the Orlando World Center Marriott

Abstract

A life-threatening
flash fire can result from “accidental” ignition of a dense cloud of
combustible dust, where the concentration of dust in the cloud exceeds the
Minimum Explosible Concentration.  Dense dust clouds can arise from several
sources, including (1) emptying bags and boxes of dusty materials into mixers,
reactors, or product-recovery vessels; (2) cleaning ductwork; (3) emptying dust
collectors; (4) emptying dryers; (5) release of dust accumulations from
elevated surfaces, following a primary explosion or other “mechanical shock”
event; (6) vigorous sweeping of large accumulations of dust on floors; and (7)
failure of dust-conveying ducts, piping, boots, or sleeves. 

Where
operators, mechanics, and contractors could be exposed to relatively-large
dense clouds of combustible dust, they should be protected from possible flash
fire.  In addition to the eye, head, foot, and hand protection that is typical
for chemical plants, they should be wearing clothing that would resist ignition
from a flash fire.

Data are
available for the intensity of flash fires, as functions of the weight of
combustible dust and the heat of combustion, in terms of kilowatts per square
meter.  Thus, there is a correlation between housekeeping – to limit the
accumulation of combustible dusts on floors and elevated surfaces – and the appropriate
flame resistance of clothing.

Good guidance
is given for protection from flash fire for flame-resistant [“FR”] clothing,
particularly where the hazard is “arc flash” and where compliance with the NFPA
70E standard is involved. With the available data, the degree of protection needed
against thermal radiation for a wide variety of flash-fire circumstances, is
given in this presentation.