Page 20 - OHS, September 2020

PPE: ELECTRICAL SAFETY
Understanding NFPA 70E and NFPA 2112 FF Standards
A deep dive into the NFPA 70E and 2112 flash fire standards, and how you can best use them to fit your workers with PPE.
BY CHRIS COTA
For workers whose jobs put them in the hot zone, flame-resistant (FR) clothing is one of the most important tools in their arsenal. Oil and gas, electricians, line workers, chemical
plant workers and people in other similar industries are all at risk of coming into contact with an arc flash or flash fire hazard every day on the job.
Arc Flash vs. Arc Fire
Arc flash explosions are short, intense bursts of energy that can reach temperatures four times hotter than the surface of the sun (think 35,000 degrees Fahrenheit), even though they only last for just a fraction of a second. A flash fire is a sudden, intense fire caused by ignition of a mixture of air and a dispersed flammable substance such as a solid, flammable or combustible liquid, or a flammable gas. It is characterized by high temperature, short duration and a rapidly moving flame front.
The initial burst is not the only dangerous component of a flash fire. Contrary to what you may have heard, among workers who have survived flash fires/explosions, the most severe burns are found on the areas that were covered by their regular (non- FR) clothing and not on their uncovered head and hands, as most people believe. The burning clothing,
in contact with the skin and continuing to burn long after the flame has retreated, causes the most severe burns. Clothing that melts without burning can also cause significant damage.
What Not to Wear When
Fire Hazards Are Present
A worker not wearing the appropriate flame-resistant PPE can suffer serious, life-threatening burns if his or her clothing catches fire, continues to burn after exposuretoflameorbeginstomelttotheskin.Thisis why OSHA “prohibits workers from wearing clothing that, in the presence of an arc, can potentially increase the extent of injury; that is, if the clothing would ignite and continue to burn, or if it melts on the skin.” That means workers are “generally prohibited from wearing clothing materials made entirely of, or blended with, synthetic materials such as acetate, nylon, polyester, or rayon.”
OSHA goes on to say that “clothing made from 100% cotton or wool may be acceptable if its weight is appropriate for the flame and electric arc conditions to which a worker could be exposed. As heat levels increase, these materials will not melt, but they can ignite and continue to burn. The amount of heat required to ignite these materials is dependent upon a
The Hazards, Explained
HAZARD
ARC FLASH
* Dangerous release of energy created by an
electrical fault (very short duration—fraction of
a second)
* Can reach 35,000 degrees Fahrenheit (19,400
degrees Fahrenheit) – four times hotter than the surface of the sun
FLASH FIRE
* A sudden and intense fire that is caused when
a mixture of air and a flammable substance
combine to ignite
* Extremely high heat, short duration (typically less
than three seconds), and a rapidly moving flame
HOW IT OCCURS
* High current source with a conductive object can cause electricity to flash over
* Dropping a tool or otherwise creating a spark can ignite an arc flash in an area around a conductor
* Equipment failure
* Breaks or gaps in insulation
* Dust, corrosion, or other impurities on the
surface of the conductor
IGNITION OF A COMBUSTIBLE ATMOSPHERE FLASH FIRES NEED THREE THINGS TO OCCUR: 1. Oxygen
2. Ignition Source
3. Fuel
Flash fire conditions worsened in confined spaces
CAN PRODUCE
* Thermal Radiation * Intense Light
* Acoustical Energy * Pressure Wave
* Debris
* Very intense, fast moving flame
* Pressure waves (in closed environments) * Ignition of surrounding area contents
INDUSTRIES AFFECTED
ELECTRICAL; UTILITY
* Installation, Repair & Maintenance
of Electrical Systems
PETROCHEMICAL; OIL & GAS
* Any operations around flammable gases,
volatile liquids, or particulate
16 Occupational Health & Safety | SEPTEMBER 2020
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