When the Dust Settles

Areas of Concern

For powered industrial equipment, a number of factors must be considered to determine the appropriate level of equipment ignition-source protection and surface-temperature limitation requirements:

• The type of dust material;

• Is the dust conductive or combustible?;

• The cloud ignition temperature (Cloud AIT - °C/°F);

• The 5-millimeter or ¼-inch layer auto ignition temperature (Layer AIT - °C/°F);

• The minimum spark energy required to ignite a dust cloud (mJ).

Depending on the type of power source within the equipment, the following dust ignition sources must be addressed on powered industrial vehicles used in dust hazardous areas.

Electrical Equipment

Arcs or sparks may arise from unprotected electrical equipment, such as starters, motors, batteries and instrumentation. The vehicle should be supplied with electrical equipment suitable for use in explosion hazardous areas, depending on the level of protection required. The temperature classification of the equipment should be checked to ensure it is appropriate for the range of dust and fibers likely to be encountered.

Care should be taken to ensure that vulnerable items, such as lights, are durable enough to withstand normal and arduous wear and tear.

Electrical equipment may be eliminated by the use of mechanical alternatives, such as mechanical fuel, temperature and pressure gauges or starters operated by spring recoil, hydraulic fluid or compressed air.

Equipment may be fitted with electric starters and wired to a plug-and-socket connection for use with a starter battery that is stored and used in a safe area.

Surface Temperature

The surface temperature of the engine, exhaust, electrical equipment, brakes and any other hot spots on the vehicle should be kept below the lowest ignition temperature of any flammable materials likely to be encountered. The supplier will provide details of the maximum surface temperature that may be achieved by the truck in normal operation.

The exhaust manifold and associated piping may be cooled by using a water jacket or water-cooled heat exchanger, by passing the exhaust gases through a water bath or by air cooling. Water levels should be monitored regularly and maintained at the recommended level.

Air cooling may be provided for hot spots, such as the friction surfaces of brakes and clutches and the outer casings of electrical equipment. In extreme cases (for example, a truck required for heavy work cycles in an area where materials with a low ignition temperature are present), oil-filled or labyrinth-type brake enclosures may be required.