Static Electricity

Research shows that flame resistant garments are no more hazardous than any other apparel in hazardous areas where static electricity is a concern.

The generation of static electricity on clothing depends on a number of factors: the relative humidity, the fabrics involved, the use of grounding devices, and the task being performed. Under standard environmental conditions, synthetic fabrics such as polyester or NOMEX absorb less moisture and retain more static than natural fiber fabrics. NOMEX IIIA contains 2% static dissipative fiber to control nuisance static. NOMEX does not require moisture in the atmosphere to conduct static electricity. However, NOMEX garments alone without other engineering controls will not address the hazards associated with static.

Natural fabrics such as cotton used in Bulwark Excel-FR and Excel-FR ComforTouch garments have less static buildup in high humidity conditions because they absorb water from the atmosphere. This water conducts and helps distribute the static charge. However, since absorbed water is actually conducting the charge and not the cotton fiber itself, cotton fabric is ineffective at dissipating static charges at low levels of relative humidity (<20% RH). These garments will dissipate static in high humidity, but not under low humidity conditions.

Static electricity in the workplace can be either a nuisance in the form of garment cling, or a hazard from sparking in a flammable atmosphere. The primary hazard from static charges is the stored energy on the body of an ungrounded person. Most flammable vapor/air mixtures can be ignited with spark energies in the range of 0.15 to 2 millijoules (.001 joule, a unit of electrical energy). The ungrounded human body can store energies as high as 40 millijoules while clothing can hold less than 5% of that amount. The contribution of clothing to static charge buildup is very small as long as wearers do not don or remove items of clothing in a hazardous area.

Donning or removing any garments can generate static charge on the fabric through triboelectric generation by friction and cause charge separation between the layers of clothing. Increased charge on the fabric and charge separation increases the likelihood of spark generation from the fabric surface. Testing of a Bulwark vest showed a 5X increase in static charge to the wearer when the vest was removed compared to the charge present while the vest was being worn. Therefore the action of donning or removing garments can increase the charge on the human body and provide a source of spark energy.

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How flame-resistant fabrics work

Flame-resistant (FR) fabrics and garments are intended to resist ignition, prevent the spread of flames away from the immediate area of high heat impingement, and to self-extinguish almost immediately upon removal of the ignition source.

Normal work apparel will ignite and continue to burn if exposed to an ignition source such as flame or electric arc. Everyday fabrics will continue to burn until they are extinguished or all flammable material is consumed.