Storing flammable liquids

How to properly use storage cabinets for flammable and combustible liquids in industrial facilities.

BY SIMON FRIDLYAND

Flammable and combustible liquids are widely used by maintenance people in their daily work. The storage, dispensing and usage of such liquids are regulated by fire codes as well as occupational health and safety laws. The regulations allow the storage of flammable/combustible liquids in plants in the following areas:
* Specially designed storage rooms, in closed containers only, where dispensing is not allowed.
* Specially designed storage and dispensing rooms, where dispensing is allowed (in this instance, the room must be equipped with explosion-relief walls and meet other requirements).
* In the open, in closed containers only, with very limited quantities in situations where handling of flammable and combustible liquids is secondary to the primary activity of manufacturing.
* Storage cabinets.
This article focuses only on the storage of flammable and combustible liquids in storage cabinets. The cabinets for storing flammable/combustible liquid containers serve the following purposes: the protection of flammable/combustible liquids against flash fires; the prevention of excessive internal temperatures in the presence of fire; and the containment of spilled flammable liquids to prevent the spread of fire.
Flammable/combustible liquid storage cabinets must bear ULC or cUL labels as evidence for compliance to Canadian standards. The cabinets are usually made of metal having a double wall construction with a three-point door latch and a liquid-tight door sill raised at least 50 mm above the floor.
Storage cabinets also are usually equipped with vents, which are normally plugged by the cabinet manufacturer. While cabinet manufacturers may provide facilities for venting, ventilation for flammable storage cabinets is not required or recommended. Venting a flammable storage cabinet is not necessary for fire protection purposes. Flammable and combustible liquid storage cabinets are designed to protect the internal contents from a fire outside the cabinet. An improperly vented cabinet could compromise the ability of the cabinet to protect its contents from a fire.
According to NFPA 30 (Flammable and Combustible Liquids Code) 6.3.4, “The cabinet is not required to be vented for fire protection purposes. However, the following shall apply: (a) If vented for whatever reasons, the cabinet shall be vented outdoors or to the fume hood exhaust duct in such a manner that will not compromise the specific performance of the cabinet. (b) If the cabinet is not vented, the vent openings shall be sealed with the bungs supplied or with bungs specified by the manufacturer.”
If the users decide to vent a cabinet, at the very minimum, venting must incorporate the following steps:
* Remove both metal bungs from the sides of cabinet and replace them with flame arrester screens (normally these come with the cabinets).
* Connect the bottom opening to the exhaust system using rigid metal piping equivalent or better than that used in the construction of the cabinet. Cabinets shall not be vented directly into the fume hood. Piping must have an inner diameter no less than that of the opening and be threaded to match the hole that’s manufactured into the cabinet. If needed, piping may have to be welded in place. Riveting or fastening into the cabinet may compromise the fire protection rating of the cabinet. PVC or plastic piping shall not be used since it cannot withstand high temperatures, such as in a fire.
* The top opening will serve as the fresh-air inlet. The make-up air should be supplied to the fresh-air inlet through piping similar to that used for the exhaust.
* The total run of the vent piping should not exceed 25 ft in length.
* Do not manifold vent piping from multiple cabinets.
* The fan used to ventilate the cabinet must be rated as intrinsically safe.
Cabinets are not required to be grounded. Many manufacturers provide a grounding screw on their cabinets as a convenience to the user. The user can connect this screw to a building ground and use the cabinet-mounted ground point as needed to ground individual containers.
A maximum quantity of 500 litres of flammable and combustible liquids may be stored in an approved cabinet, of which not more than 250 litres may be Class I liquids. The fire code allows storing up to three cabinets in a fire compartment. A fire compartment means an enclosed space in a building that is separated from all other parts of the building by enclosing construction that provides a fire separation having a required fire-resistance rating.
In industrial occupancies, quantities of flammable liquids and combustible liquids greater than those specified above are permitted in a single fire compartment, where: (a) the total quantity stored in a group of cabinets is not more than the quantity permitted for three cabinets, and (b) the distance between groups of cabinets described in Clause (a) is not less than 30 m.
In order to properly assess the situation, one must understand the boundaries of a particular fire compartment and take into account all flammable and combustible liquids present there. They shall not exceed the maximum quantities.
The best way to identify the boundaries of a fire compartment is to review the architectural drawings of the facility. They would identify fire separations having a fire-resistance rating.

Simon Fridlyand, P.Eng., of SAFE Engineering Inc., specializes in industrial health and safety concerns and PSR compliance. For more information, visit www.safeengineering.ca.

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