OHS Code Explanation Guide

Published Date: July 01, 2009
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Part 36 Mining

Section 543 Flammable gas monitors

Subsection 543(1)

This subsection requires the installation of gas monitors in any location that can be classified as a hazardous location according to section 18 of the Canadian Electrical Code. In part, section 18-004 states that:

“Hazardous locations shall be classified according to the nature of the hazards, as follows:

(a) Class I locations are those in which flammable gases or vapours are or may be present in the air in quantities sufficient to produce explosive gas atmospheres;
(b) Class II locations are those which are hazardous because of the presence of combustible or electrically conductive dusts;
(c) Class III locations are those which are hazardous because of the presence of easily ignitable fibres or flyings, but in which such fibres or flyings are not likely to be in suspension in air in quantities sufficient to produce ignitable mixtures.”

In mining operations a hazardous location can exist in an underground mine, conveyor gallery, reclaim tunnel, storage silo, drying plant, heating furnace, electrical room, battery charging room or other similar location.

Gas concentrations in hazardous locations can increase suddenly and trigger an alarm. Such an alarm is only effective if it prompts an immediate response. This may not occur if the monitoring device gives only a local alarm, but will occur if it is linked via a remote control and monitoring system to a permanently attended communication station. Such stations are typically found on the surface in the mine offices. They are computer controlled with comprehensive visual and audible alarm systems.

The general expectation under this subsection is that monitoring for flammable gases takes place at every location that is classified as a hazardous location as the result of a hazard assessment. It is further expected that a continuous monitoring system will be used, linked to a permanently attended communication station. Where necessary, the mine electrical inspector is available to provide guidance and interpretation of the OHS Code and the Canadian Electrical Code. Readers are referred to the explanation to section 165 for additional information about hazardous locations.

Subsection 543(2)

The alarm given at a permanently attended communication station by flammable gas monitors can be visual, audible or both. Frequent calibration of these instruments is critical to assuring their proper function and accurate reading. Note the requirement that the alarm must sound when the gaseous content of the atmosphere exceeds 20 percent of the lower explosive limit of the gas being monitored. Since the lower explosive limit varies depending on the physical characteristics of the particular gas, the remote control and monitoring system must be programmed accordingly. Workers must be trained to correctly use the related monitoring device.