The proper arc flash PPE (personal protective equipment) is vital when an electrician is in danger of being injured by an arc flash.
An arc flash can happen any time an electric arc is supplied with enough electricity to cause injury, damage or fire.
Electrical arcs fed by controlled energy and in limited quantities are used in welding and other industrial applications, and can also produce very bright light, as in arc lamps with either enclosed or open electrodes.
The temperature on arc flashes can reach, and in some cases exceed 20,000°C (35,000°F) at the arc terminals. The massive release of energy in the fault will vaporize the metal conductors quite quickly, resulting in molten metal blasting and expanding plasma outwards with powerful force.
Typically, arc flash incidents are inconsequential, and no harm comes to the electrician, especially when wearing proper arc flash PPE, but it is possible for a flash to produce a very severe explosion.
In these cases equipment is destroyed, a fire can start and workers are injured. Not just the one involved in the incident, but any one in close proximity, as well.
In addition to the explosive blast of an arc flash, even more destruction can arise from the intense heat the arc produces. The metal plasma arc is capable of producing a tremendous amount of light energy that can range from ultraviolet to far infrared.
The surface of any nearby object is instantly heated to extreme temperatures, including people, which has devastating effects.
In most cases, an arc flash incident capable of igniting clothing is highly unlikely with systems operating below 208 volts phase to phase or 120 V to ground, if fed by a transformer that is less than 125 kVA.
This is because 120 volts doesn’t provide enough potential for an arc flash hazard to occur. However, 480 V electrical services do have the capacity, and can cause an arc flash hazard.
Any equipment above 600 V has a higher energy, which means it has a greater possibility of becoming an arc flash hazard.
The basic characteristics of an arc flash blast are very different than those of a chemical explosion because an arc flash produces more light and heat, while chemicals produce more of a mechanical shock. But the devastation that results from either is quite comparable.
The arc produces rapidly expanding vapour, heated to extreme temperatures which can cause severe injuries to people and damage to equipment. The intense visible and non-visible light the arc produces can cause temporary, and sometime permanent blindness, or others types of eye damage.
The most important part of any job is personal safety. There are several ways to protect yourself from an arc flash hazard, including wearing approved arc flash PPE or altering the design and configuration of the electrical equipment you are working with.
The best way to eliminate the possibility of an arc flash hazard is to disconnect the electrical power when working with electrical equipment. However, the act of de-energizing the equipment can also be a hazard.
One of the latest solutions to this problem is to have the worker operate the equipment remotely, allowing him to stand as far away from the equipment as possible, so if an incident does occur, no one will be hurt.
There are many companies offering arc flash PPE. All materials used to make this equipment must be tested to establish their arc rating. Which is the maximum amount of energy it can withstand before reaching the breaking point.
The arc rating is generally described as cal/cm² (which means small calories of heat energy per square centimetre). Modacrylic-cotton blends are among the best fabrics to protect against arc flash hazards.
It is important to use the correct PPE for the task you are going to perform. You can find out what you should wear in NFPA 70E under the hazard classification table.
The table lists most of the electrical tasks you are likely to encounter, according to voltage level, and what type of PPE you should wear, by category.
For example, say you are assigned to work on a 600 V switchgear where you will have to remove the cover, and expose bus bare, live parts, the table recommends wearing a category 3 PPE system. This system is made up of several pieces of protective clothing that together will provide up to 25 cal/cm² of protection.
Category 3 PPE system includes:
Arc flash PPE is designed to protect you in case an arc flash incident occurs, and should therefore be considered as your last line of defence. It is always better to do everything possible to reduce the possibility of an incident occurring in the first place, or at least reducing the severity of the incident.
This can be achieved by thoroughly assessing the arc flash hazard and using high-resistance grounding technology, which has shown to dramatically reduce the severity and frequency of incidents.