OHS Code Explanation Guide

Published Date: July 01, 2009
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Part 36 Mining

Section 538 Light metal alloys

The general expectation of this section is that the use of light metal alloys in underground coal mines is restricted. This reflects the hazard of light metal alloys becoming a source of potential ignition of gas or dust.

Subsection 538(1)

The term “light metals” refers to metals containing aluminum, magnesium and/or titanium, including aluminum paint and aluminum cans. Products containing these metals are generally not allowed in underground coal mines or other hazardous locations. Friction or sparking resulting from light metals striking or being struck by oxidized (rusty) ferrous metal is enough to ignite a mixture of methane and air.

The specific definition of the various light metals and their percentages in alloys is based on that of the former National Coal Board (NCB) of the United Kingdom (UK). Readers are referred to (i) NCB Spec No 481, CENELEC 1977 & (ii) Light Alloys Fact Sheet, on webpage: web.cim.org/ugcoal/). The use of aluminum was restricted, but not prohibited, in the UK following 12 international incidents that occurred between 1950 and 1955 and one in 1962. Ten of these incidents resulted from the use of aluminum face supports and one involved auxiliary fan blades.

Restrictions on the use of light metal alloys in underground coal mines and similar hazardous locations are intended to prevent light alloy metals from being struck by rusty iron or steel. For example, British Columbia restricts their use to the following:
(a) electrical equipment within a flameproof enclosure;
(b) use in circumstances when there is no possibility of friction or impact;
(c) adequate coating with non-sparking material and immediately removed from service if the coating is damaged; and
(d) handheld tools which are placed in a non-sparking storage container following use.

(See Health, Safety and Reclamation Code for Mines in British Columbia (2003) Section 6.43.3 Prohibited Metals.)

Subsection 538(2)

It is impossible in some instances to prohibit the presence of all light metals. For example, many common fire extinguishers are made with light metals, but are required as fire protection underground. In these instances, equipment with aluminum components must be equipped with a protective canopy or other measure that serves to prevent friction or impact on the light metal.

Subsection 538(3)

The use of fan blades made of light metal alloy needs to be restricted in underground mine ventilation fans because light metal alloys can cause incendiary sparking when struck by oxidized ferrous metal (rusty iron). If a spark was created at a time when high explosive levels of methane gas were present, a catastrophic explosion could occur. Restrictions typically require protective coatings with a non-sparking material and periodic inspection to identify and repair damaged coatings. (See Health, Safety and Reclamation Code for Mines in British Columbia (2003) Sections 6.36.3 and 6.36.4.)

Subsection 538(4)

Potentially explosive atmospheres occur not only in underground mines but also at surface facilities where potentially explosive dusts are present. Therefore light metal alloy restrictions apply there as well. Examples of such hazardous locations include coal preparation plants, coal silos or underground reclaim galleries beneath surface coal stockpiles and in small ventilation/cooling fans within some surface buildings.