Page 16 - Occupational Health & Safety, September 2018

INDUSTRIAL HYGIENE
plosion? A dust explosion can only occur when the following five factors are present (see figure 3):
■ Fuel, in the form of dust particles
■ Dispersion of the fuel in the form of a dust cloud
■ Oxygen in the form of air
■ Confinement of the dust cloud in the form of a container (e.g., a dust collector)
■ A source of ignition
Figure 3: Explosion Pentangle (courtesy of AAF International)
Dispersion could, for example, be as a result of a dry filter being pulse cleaned or, according to OSHA,6 from an initial (pri- mary) explosion in processing equipment causing a blast wave that disturbs accumu- lated dust that, if ignited, causes a second- ary explosion. The latter is often far more
destructive than a primary explosion due to the increased quantity of dispersed dust (figure 4).
Should monitoring dust concentration also be part of the mitigation?
Undertaking a walk-through survey using a hand-held, real-time sampler would give instantaneous indication of concentration. It also could be used to check the effectiveness of control mea- sures, such as local exhaust ventilation (e.g., pre and post filter).
Industrial hygienists may already be undertaking personal monitoring for toxic or sensitizing dusts, and the same air sam- pling pump could be used in combination with a real-time sampler when housed in a robust, portable case, on an unattended, short-term basis. Such a system can provide
concentration using a gravimetric filter but also a time history profile, which could help identify the source of the problem.
Fixed, AC-powered solutions also could be used on a continuous basis for high-risk areas. These have the advantage that the data can be made available remotely using a web-based interface. These systems pro- vide real-time alerts via text message or an email, should limits be exceeded. Reports can easily be automated and sent to mul- tiple users, which allows for an early inter- vention to avoid a potential problem.
Great care should be taken in hazardous atmospheresthatmayrequireinstrumenta- tion to be intrinsically safe or require a hot- work permit, and action thresholds should always be set at a fraction of the lower ex- plosion limit (LEL) for the dust in question. But if there is any doubt whatsoever, ensure that you speak to the relevant site manager or supervisor who has responsibility for risk assessment and permitting and who can advise accordingly.
Summary
Dust explosions continue to be a persis-
16
Circle 34 on card.
Circle 31 on card.
www.wisesafetyenv.com
Are you ready?
OSHA’s Silica Rule is now in force for General Industry & Maritime as well as Construction
3M has respirators for every risk level of Respirable Silica Dust
Higher APF levels available
For more information
St. Louis Wise . . . . . 800-727-8541 St. Louis Reis . . . . . . 800-777-7347 Boston. . . . . . . . . . . . 877-257-3263 Denver . . . . . . . . . . . 800-677-7347 Houston . . . . . . . . . . 800-234-2377
Combustible Dust Te
Experience the WISE AdvantageTM
Experts in Combustible Dust - Prevention & Mitigation -
FAUSKE & A S S O C I A T E S, L L C
APF-50
Jacksonville . . . . . . . 877-655-7347 Kansas City . . . . . . . 800-255-1101 Little Rock . . . . . . . . 800-901-4678 Louisville . . . . . . . . . 502-637-4337 Salt Lake City. . . . . . 800-559-7347
APF-10
e,
A
NFPA 652 DHA Training Next Class: November 13-14, 2018
Dust Hazards Analysis (DHA)
www.fauske.com dust@fauske.com +1 630 323 8750
AP
A
5
P
P
PF
F
-
-2
25
Check out our video guides
s including: “How to Collect a Dust Sample”
e
s
s
o
o
n
t
t
n
l
i
i
n
n
l
i
i
n
n
e
g
g