When the Dust Settles

Thermal sensors may also be used to detect overheating. These may be used to trigger audible or visual alarms and to provide automatic shutdown of the vehicle/engine.

The use of insulation cladding to provide protection from hot surfaces is not recommended because it is liable to be damaged and may be penetrated by flammable dust or fibers.

Spark-Producing Components

Non-electrical items can cause electrostatic or frictional ignition by rubbing or impact. Therefore, adequate clearance is needed between fixed and rotating parts, with allowance made for engine movement during normal operation. Engine-cooling fans should be made from non-metallic material, such as plastic.

The use of aluminum, magnesium, titanium and light alloys is generally minimized because of the risk of sparks from a thermite reaction (which may occur on impact between light metals and rust). If such components are used, they must be shielded from impact by an enclosure. Surface coatings incorporating these materials are normally considered unsuitable.

The risks of sparks from static build-up are minimized by the use of electrically conducted materials for drive belts, tires and other components.

The load contact points of the equipment may cause frictional sparks when they contact a metal drum or other object or are allowed to impact on concrete floors. They are often fitted within brass or stainless steel sleeves.

Spark arresters are also used to prevent any spark from the exhaust system reaching the outside atmosphere. Both inlet and exhaust systems are designed to withstand internal explosions.

Dust Ingestion

Ingestion of flammable dust may result in reduced engine performance and increased carbon emissions from the exhaust. Installation of a multi-stage dust filter is recommended. The filter should be cleaned on a regular basis.

Unfortunately, codes, regulations, construction specifications and testing procedures to ensure safe operation of powered industrial equipment in explosion hazardous dust areas have never been developed in the United States. Regardless, OSHA and NFPA guidelines endorse and sometimes enforce the use of equipment types, which according to UL, have not been tested, certified or found suitable for use in these dust hazardous areas. This contradiction may leave equipment users and operators in the dust when it comes to equipment fire safety.

Robert Zuiderveld is general manager at Pyroban Corp., a provider of safety and environmental solutions.