OHS Code Explanation Guide

Published Date: July 01, 2009
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Part 36 Mining

Section 716 Seals

Subsection 716(1)

Worked out areas of a mine can still present a significant hazard to underground coal mine workers. Of particular concern is the potential for gases or water to accumulate or for the spontaneous combustion of coal or coal dust, resulting in fire and/or explosion. For this reason worked out or inaccessible areas must be securely sealed off. In exceptional circumstances there may be good reason not to seal old areas, but this practice must be approved in writing by the Director.

Subsection 716(1.1)

Seals required under subsection (1) must be built to withstand over pressure effects created by any subsequent explosion within the sealed areas. The minimum levels required are based on those recently introduced in the U.S. These minimum levels are an over pressure of 345 kPa (50 psi) for monitored seals. If such seals are designed to also contain a known or suspected fire under subsection (4), then minimum seal design requirements increase, for example, to a minimum over pressure of 800 kPa (120 psi) for unmonitored seals, rising to an over pressure of 4.4 Mpa (640 psi) if an explosion pulse can be expected.

Subsection 716(2)

Since time is the critical factor in preventing the accumulation of dangerous gases or water or the generation of spontaneous combustion, this subsection requires that such abandoned areas be sealed off within three months of mining activities ceasing in those areas.

This subsection allows the Director to approve an alternative, but such an approval would typically be provided only in exceptional circumstances.

Subsection 716(3)

Although a properly designed seal minimizes potential hazards to mine workers, knowledge of what is happening behind a seal is also critical to worker safety. For this reason the employer is responsible for ensuring that such behind-the-seal conditions are regularly monitored. Where warranted, the employer must also take actions to ensure that hazardous conditions are mitigated or eliminated. Where mitigating actions cannot be safely implemented, mine worker’s health and safety must be the prime consideration when determining the next steps to be taken.

Subsection 716(4)

If a seal is being constructed to contain or isolate a fire or spontaneous heating, it is quite logical that it also be designed to withstand the effects of an explosion within the sealed area. Such seals are substantial structures and must be designed by a professional engineer guided by best industry practice considering the over pressure levels outlined in subsection (1.1). It must be also be possible to sample the atmosphere or drain accumulated water from behind a seal. Sampling can provide advance warning of gas buildup and provide a means of mitigating any problem related to water accumulation.