High hazard sites where electric security fences have been installed include petro-chemical plants, fuel and gas tank farms, airports, toxic waste disposal sites, and a variety of other industries that use volatile materials.

The main concern on such sites is the possibility of a short on the electric fence generating a spark that could ignite flammable liquids, vapours, dusts or gas.

AS / NZS 3016: 2002 - the Australia / New Zealand Standard relating to the installation of electric security fences cites the following on this subject:

• 3.9 Hazardous Area – area in which an explosive atmosphere is present or may be expected to be present, in quantities such as to require special precautions for the construction, installation and use of electrical equipment

• 6.0 Fire Risk – Experience indicates that vegetation or other plant material touching an electrified fence wire will normally not ignite and present a fire hazard. However, under certain unusual conditions, wires within 20mm of earthed metal, such as other fence wires or metal parts, can ignite dry plant material.

To reduce this risk in areas where fires may be a hazard, it is recommended that:

(a) Separation between exposed electrified wires and earthed metal be maintained at 30mm or greater, measured along the shortest air path: and

(b) Fence lines be kept well maintained and free from vegetation and other plant material.

AS / NZS 3014: 2003 – the Australia / New Zealand Standard relating to the installation of any type of electric fence adds the following:

• 5.6 Electric fence wires and energizers shall not be installed in areas ( e.g. petrol or fertilizer storage areas) where flammable gases or dusts may be present

What does this mean in practical terms?

The most important point is that electric fences should not be built in or near an enclosed space where dangerous materials are present. In reality this is an unlikely scenario because fences are invariably built on the boundary of a property and as such would usually be well away from the buildings, valves or pump stations where there may be danger.

The issue of fence line shorts is also generally not a problem on high hazard sites because apart from the distance factor the fences are also frequently built with concrete nibs and there would not be any inflammable material like dry grass near the fence.

However it is very important for the contractor installing such fences to negotiate a service contract with the customer to ensure the fence and fence line are maintained to a high standard. Such good housekeeping ensures the products will continue to work well and that any risk to the site is minimized.

Finally it is worth pointing out that the Security Manager of the New Zealand Oil & Gas Terminal was exactly right in stating that he considered his 8 sector electric security fence system the best form of fire insurance: “The fence is extremely effective in keeping people off the site and in our experience people are the biggest fire risk to our facility.”