DS 7-76 Prevention and Mitigation of Combustible Dust ... - FM Global

7-76 Combustible Dust Explosion
Page 10 FM Global Property Loss Prevention Data Sheets
e) Obstruction by pipes, wires, or other utilities
f) Permanent or temporary equipment located next to the venting device
Any of these can increase effective vent-relief pressure (P stat) and cause explosion-resisting walls to fail
and/or damage the building structure during an explosion.
2.3 Equipment Explosion Hazards
2.3.1 General
2.3.1.1 Locate all equipment having an explosion hazard outdoors whenever practical (3.1.2).
2.3.1.2 Where equipment has an explosion hazard, take one of the following steps:
OR
a) Eliminate the explosion hazard using any of the techniques detailed in Section 2.3.2,
b) Mitigate the explosion hazard using explosion venting, suppression, containment, or vacuum operation,
or a suitable combination of these, as detailed in Section 2.3.3.
2.3.2 Explosion Hazard Elimination
2.3.2.1 Where equipment handles coarse material, prevent dust from being generated during material
handling by suitable methods or preclean the coarse material to remove all fines from most of the process
equipment.
2.3.2.2 Where equipment handles coarse material, prevent dust from being generated during material
handling by eliminating airborne dust inside the processing equipment using a liquid mist (water or other
compatible liquid) as follows:
a) Apply the liquid suppressant at a point in the process that involves substantial turbulence, e.g., at a
discharge spout, to ensure the suppressant is thoroughly mixed in with the material stream.
b) Install an interlock that will shut down the solid process stream on suppressant spray-system malfunction
if this system is being relied upon as the sole means of hazard control.
c) Confirm the effectiveness of the system to eliminate dust in the equipment by visually checking
equipment while it is running, for example, by opening access or inspection ports.
d) Develop a maintenance and inspection program with written procedures and records of completion to
ensure the dust-suppressant spray system is functioning properly whenever the solid process stream is
being handled.
2.3.2.3 Inert the combustible dust by mixing it with a noncombustible dust (known as ‘‘phlegmatization’’)
on the following basis (3.1.3):
a) Perform a test to determine the mixture is non-explosible per ASTM E1515, Standard Test Method
for Minimum Explosible Concentration for Combustible Dust or international equivalent.
b) Ensure the noncombustible dust does not separate from the combustible dust during further material
handling.
2.3.2.4 Reduce the oxygen level in the process with an inert gas in accordance with recommendations in
Data Sheet 7-59, Inerting and Purging of Equipment.
2.3.2.4.1 If values of the Limiting Oxygen Concentration (LOC) are not available from Data Sheet 7-59 for
the particular material being handled, arrange for laboratory testing of materials to determine the LOC.
2.3.2.4.2 Where an inert atmosphere is to be used to safeguard pneumatic conveying of freshly ground or
freshly manufactured light metal powder (aluminum, magnesium, titanium, zirconium):
a) Provide a minimum oxygen concentration of at least 1% to ensure a stable oxide layer can be formed
to passivate the dust.
b) Where the metal powder is not to be exposed to air, or where testing has shown a lower oxygen level
is acceptable, concentrations lower than 1% are acceptable.
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