Protective clothing for electrical arc flash hazards

An arc flash (or arc blast) occurs when a high amperage electric current arcs through air as a result of phase-to-phase or phase-to-earth contact. This transmission results in the production of localised temperatures of up to 20000°C; hotter than the surface of the sun. A typical duration for an arc flash is less than 1 second.

Accompanying this heat release is a high energy pressure wave, similar to a traditional explosion. The propagation of this pressure wave can result in workers being forcibly thrown through the air and other heavy objects becoming projectile hazards. The interaction of the extreme heat and pressure wave can cause melting of metallic components and spraying of molten metal droplets to distances of 3 metres or more. These metal droplets are a secondary flammability and projectile hazard.

Increasingly, workers at risk of arc flash exposure are being issued garments made from highly technical FR (flame resistant) fabrics such as Nomex† or Proban‡ treated cotton.

In the US, the use of arc rated clothing and voltage rated gloves in electrical tasks in the workplace has contributed to a 57 per cent decline in electrical fatalities since the introduction of OSHA 1910.269 in 1994 and NFPA 70E in 1995.

The appropriate Scotchlite Reflective Material to attach to these garments is 3M Scotchlite Reflective Material 8935 Flame Resistant Fabric.

When exposed to flame or sufficient heat, flame resistant reflective materials will combust but are certified to self-extinguish within 2 seconds of the ignition source being removed. In addition to this, when burned the material must not yield molten or flaming debris.

Garments made from untreated 100 per cent cotton thread are not flame retardant and will ignite and combust rapidly at temperatures above approximately 250°C. Appropriate weight untreated cotton garments are traditionally considered an acceptable garment for live electrical work because during arc exposure cotton may char and/or burn but will not yield molten debris, unlike polyester or other non-FR synthetic fabrics. While flame resistant reflective materials are not strictly necessary on a non-FR garment, their use should be considered in order to minimise any potential additional hazard posed by reflective material ignition.

The ATPV (Arc Thermal Performance Value) and the EBT (Energy Break Open Threshold) are the most commonly used parameters to evaluate the level of protection of arc rated clothing. The ATPV for 3M Scotchlite Reflective Material 8935 is 11.9cal/cm². The addition of the reflective material on the garment will provide extra protection under the trim covered portion of the garment. However, the total garment protection may not have a significant benefit from the added reflective material since it covers a small portion of the body.

Under the extreme circumstances of an arc blast, no garment can be expected to fully protect a worker. However, careful garment selection can help ensure additional hazards are not introduced due to the behaviour of workwear in an arc incident.

Use the contact form to request 3M Scotchlite Reflective Material Section Guide.

*This information is provided for information only and should be used in conjunction with relevant industry standards and/or guidelines.
† Nomex is a trademark of E I DuPont De Nemours
‡ Proban is a trademark of Rhodia UK Limited