OHS Code Explanation Guide

Published Date: July 01, 2009
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Part 36 Mining

Section 738 Combustible gas detector

Subsection 738(1)

This section deals primarily with the provision, installation and performance of combustible gas monitors used on coal cutting machines. Maintenance of monitoring devices is extremely important, as is regular testing of the accuracy of their readings. Coal cutting machines require a reliable, proven device to monitor the concentration of methane near the face.

Subsection 738(2)

The cutting operation generates significant quantities of coal dust and methane, and often produces sparks.  Although water spray is used to control these hazards right where the cutting operation takes place, the situation remains challenging and dangerous. Continuous monitoring of methane near the cutting head is extremely important to worker safety and confidence. The worker operating a coal cutting machine must keep the combustible gas detector operating at all times.

Subsection 738(3)

The cutting head of a coal cutting machine, such as a continuous miner, is the point at which the coal is mined and then extracted. It is the mining process that liberates methane gas that is normally contained within the coal seam. Because of the potential that the highest levels of methane gas will be present at this active mining location, this subsection requires that methane sensing devices be installed as close as reasonably practicable to the cutting head. Early detection of unusual gas levels at the cutting head will alert the operator to a potential problem, providing time for the operator to take action.

According to this subsection, the installed gas detector must be installed within three metres of the cutting head.

Subsection 738(4)

If the circumstances unique to the coal cutting machine or its application make installation of the methane sensing device within three metres impracticable, this section authorizes the Director to approve a sensor location point that is more than three metres from the cutting head. In order for the Director to make such a decision, the employer must provide proper documentation and justification.

Subsection 738(5)

Both visible and audible alarms must be provided to gain the operator’s attention quickly. The percentage of the LEL is purposely kept low to provide an early warning for workers to withdraw to a safe location. For clarity, the LEL for a methane in air mixture is 5 percent methane. The values in this section are expressed as a percentage of the 5 percent limit. For example, 20 percent of the LEL translates to 1 percent methane content e.g. 20 percent of 5 percent.

Subsection 738(6)

Since the methane detector must be interconnected with the machine control system, a methane gas excursion will trip out the cutting head. Such an occurrence would be the first warning that methane levels are rising above the levels specified in this section. Once the cutting head trips due to a high methane level, the worker must immediately back the machine away from the face and turn off electrical power to minimize the potential for initiating an explosion.