340.7 System Ducting on Combustible Dusts
•
Ducts that handle combustible particulate solids shall conform to the requirements of NFPA 91,
Standard for
Exhaust Systems for Air Conveying of Vapors, Gases, Mists, and Noncombustible Particulate Solids
, except
as amended by the requirements of chapter 3 of NFPA 68.
340.8 Ignition Sources
•
Some types of ignition sources include electric (arcs, sparks, and electrostatic discharges), mechanical
(friction, grinding, and impact), hot surfaces (overheated bearings), and flames (welding torches, and so
forth).
340.9 Vent Discharge Ducts
•
If a dust collector is located inside a building it should be located near an external wall and the exhaust from
the vent ducted to the outside.
•
The addition of a vent discharge duct can substantially increase the pressure developed in a vented
enclosure.
(See NFPA 68 Section 5-4.)
Sizing of the vent should take this into consideration.
•
Ducts that are used to direct vented gases from the vent to the outside of a building should be of non-
combustible construction and should be strong enough to withstand the expected
Pred
. Ducts should be as
short as possible and should not have any bends.
(See NFPA 68 Section 5-2.9.)
•
The duct should be less than 20ft long, have a cross-sectional area larger than the vent, and should not
interfere with the operation of the vent.
•
Bird screens or weather hoods must be low restriction and their affect should be taken into consideration
when sizing the vent area.
340.10 Vent Inspection and Maintenance
Farr incorporates two styles of explosion vents on their dust collectors. One is a rupture diaphragm and the other is
a hinged door. Explosion vents should be inspected every three months. The inspection and maintenance points are
outlined below.
General Inspection that applies to all Explosion Vents:
•
Remove obstructions such as snow, ice, dust inside and out if present.
•
Safety Decal – Replace if missing or illegible.
•
Bolts are tight – tighten and replace if missing.
•
Area around vent is free and clear of obstructions.
•
Check that flammable materials are not stored near the vent.
Rupture Diaphragm:
Rupture diaphragms have no moving parts and should be inspected for tears rips or cracks, replace if present.
Hinged Vents:
•
Open vent by firmly grasping the door at the hinge(s) and pulling hard.
•
Inspect the gasket for dry rot and leaks, replace if present. If the gasket is replaced the latch will have to be
re-adjusted. Follow the procedure in section 340.11.
•
Observe that the vent swings freely without resistance
•
Lubricate the hinge points with liquid penetrating graphite.
•
Lubricate the latch with liquid penetrating graphite.
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