NFPA 70E – 2009 Arc Flash Safety

The release of NFPA 70E-2009 has introduced several changes that directly impact the habits and practices of those workers who service energized electrical circuits.  In particular, several provisions have been made in order to prevent injury related to arc flash.

Arc flash is a hazard which occurs when the electricity in a system finds a low resistance path between the air and a worker or tool being used by a worker, causing current to arc across the gap and generate serious amounts of heat energy – in some instances, enough to vaporize metal.  Naturally, it is critical for a risk manager to reduce the chances of arc flash from occurring at a job site, and furthermore to protect those working with energized circuits from becoming injured in the event of an accident.

The newly updated NFPA guidelines have recognized that lower powered circuits do not pose a significant risk of arc flash, and as a result an arc flash analysis is no longer mandatory on any circuit rated at 240V or less when being fed by a transformer rated at 125 KVA or lower.  However, the wording of 70E-2009 has been updated to reflect the detail shown in the National Electric Code (NEC) relating to arc flash.  This includes defining when and where personal protective equipment (PPE) must be worn while working near a live circuit.

Risk managers are permitted – and encouraged – to install arc-resistant equipment and switchgear that prevents the possibility of current arcing to anyone working near it.  This is accomplished through the channeling of thermal energy by the equipment, and creates a safety sphere around the circuit where protective clothing is not required while the switchgear is latched and closed.  Once opened, a standard arc flash boundary is once again in effect.

A further set of changes have been made to the type of personal protective equipment that is allowed to be worn in an arc flash boundary (Hazard/Risk Category 1).  Denim pants and cotton clothing of any kind are no longer acceptable, due to the increased chance that they will cause second degree burns in an arc flash situation.  The new standard in PPE is arc-rated clothing that completely covers the entire body, including a face shield and leather or insulating gloves. The elimination of cotton’s status as a safe fabric is related to the deletion of the NFPA section that allowed flammable clothing to be worn as long as the energy levels involved did not surpass 2 cal/cm².  The end result is that hoods, coveralls, jackets and pants used in an arc flash boundary now need to be made of Nomex or other fabrics that are equally resistant to arc flash heat.

In combination, arc-resistant switchgear, properly rated PPE and greater clarity concerning which workplace situations require extra caution in terms of the possibility of an arc flash hazard should help to increase the overall safety and security of any facility where maintenance and repair work is regularly performed on energized circuits.