More than 70% of all the electrical injuries are triggered by arc flash explosions. An arc flash is a part of an arc fault, which usually creates a huge electrical explosion or a discharge when it takes place. Simply put, the arc flash explosions refer to the light and heat that are emitted by the explosion. Meanwhile, the pressure wave released then is called an arc blast.
In this article, we are going to show what exactly is an arc flash explosion and what its consequences are. We will also discuss the safety measures that need to be considered when working in a place with an arc flash explosion risk. Starting from the arc flash suit, we will have a look at the arc flash face shield and the PPE requirements. Finally, the article will touch upon the hazard analysis and it will provide a brief advice on what types of injuries we can find and how to offer first aid in such cases.
What Are Arc Flash Explosions?
An arc flash is, in fact, the product of a quick release of energy caused by an arcing fault. It usually happens between two phase bus bars, the second of which is neutral or a ground. It is worth mentioning that the air becomes the conductor during such an arc fault.
The arc must have enough electrical energy to trigger enough damage, injury, fire or harm. Generally, electrical arcs present a negative incremental resistance. This means that the electrical resistance will decrease as the temperature of the arc will increase.
Gradually, the arc develops and it begins to get hotter. At the same time, the resistance drops, which means that it is drawing increasingly more current. This process happens until a part of the circuit evaporates, trips, or melts. The part will allow the circuit to break and thus it will extinguish the arc.
In the following video, you can see how the engineers found at the Tyndall Air Force Base study the creation and the consequences of arc flash explosions:
Safety and Arc Flash Explosions
The main cause for which people fear arc flash explosions is the explosive blast, called the arc blast. Besides, the entire process produces an intense radiant heat. In general, surfaces tend to absorb the energy that is released by the arc, which is why arc flash explosions are so dangerous. Furthermore, they are a real hazard in working environments, and countless incidents have been reported. For this reason, arc flash safety requirements are extremely important.
Having a Safety Supervisor near the site can prove to be essential for your employees’ safety. Besides this measure, you should also know that the NFPA (National Fire Protection Association) has set some specific boundaries with the purpose of protecting employees while they work on a hazardous site.
- Flash Protection Boundary – the farthest boundary from the energy source. If a person would happen to be at this outer boundary when an arc flash occurred, they would only suffer a second-degree burn. Here, the heat would be the biggest threat.
- Limited Approach – the distance from a live part that is exposed, having a shock hazard.
- Restricted Approach – this is the approach limit at a distance from a live part. Here you will find an increased risk of shock.
- Prohibited Approach – the inner boundary is the closest distance from an exposed part. It is considered the same as making a direct contact with the dangerous area. It varies according to the equipment.
Arc Flash Suit
To protect employees from the risk of arc flash explosions, many companies make them wear an arc flash suit at work. It is a special kind of suit that protects people from burns and from the heat that is generated by the explosion. It is a great tool in reducing the risk of serious arc flash injuries. The switching suit protects people from the thermal effects that occur during such an explosion, given that it covers up the entire body.
The special arc flash clothing usually consists of the following:
- A coat and bib overalls;
- Trousers with braces (optional);
- A hood for the head, face, and neck;
- Special gloves (included if the employee must do something like live cable joining at work).
Arc Flash Face Shield
The protective face shield is designed to protect the head and the face in case of an arc flash. Usually, it is made by injection molding of a high polymer. It comes together with a buckle and a bracket for the helmet. You can choose whether you want to include mandibular protection or not, but in general, it is a good idea to go for it.
Such a shield can absorb over 99.9% of the ultraviolet radiation emitted during the arc flash. Some of them even have anti-fog coating, which is a great plus. People are worried that the shield will be uncomfortable and that it will take away their visibility. However, this is not necessarily true, since most shields come with an ultra-wide field of view. Plus, they also provide some adequate space for moving your head and protecting your neck.
Arc Flash PPE Requirements (Chart)
Given the increasing awareness in what concerns the dangers associated with an arc flash, many companies are currently offering a special type of personal protective equipment (PPE). This means that the materials are being tested for the arc rating. Arc flash rating refers to the maximum incident energy resistance a material can endure before it breaks open. The rating is usually expressed through cal/cm2 (small calories of heat energy per square centimeter).
There are two ways in which you can select the appropriate arc flash PPE, considering the task that the employee should perform. The first way is to look at a hazard category classification table, such as the one presented below. The second method refers to performing an arc flash hazard calculation, intended to see the incident arc energy that is available, which we will tackle later.
The table that you should consult before deciding on the adequate PPE is the one described in NFPA 70E. We will reproduce it here, noting that the first column indicated the hazard category, the second one the number of cal/cm2, which is the measuring unit for the incident energy, while the third shows the type of clothing required for each category.
|Category||Cal/cm2||Type of Clothing|
|1||5||FR (flame retardant) shirt and FR pants|
|2||8||Cotton underwear FR shirt & FR pants|
|3||25||Cotton underwear FR shirt, FR pants and FR coveralls|
|4||40||Cotton underwear FR shirt, FR pants and a double layer switching coat plus pants|
Table 1. Arc Flash PPE Requirements Chart
Keep in mind that besides the clothing mentioned above (arc flash shirts and pants), you will also need to include a hard hat, paired with a full-face shield as described above. Moreover, remember that PPE is the last line of protection in case an arc flash explosion takes place. Before coming down to that, you should consider how to reduce the frequency and the severity of the explosions. You can manage this with an arc flash hazard assessment.
Arc Flash Hazard Analysis
To perform such an arc flash explosions analysis, you need to collect the data about the power distribution system found in your facility. Among the information there, you will also need a scheme of the components depicted as a one-line drawing. Every device should display nameplates complete with specs. Use other details as well, such as the lengths and the cross-section area of all the cables. Don’t forget to also include information about the minimum and maximum fault currents one can expect at the entrance to the facility.
After you have all the data ready, you should perform a short circuit analysis and a coordination study. The data you obtain will then be integrated with the equations described by the NFPA 70E-2000 or the IEEE Standard 1584-2002. The equations will show you the flash protection boundary distances, as well the incident energy you need to assess the minimum PPE requirements.
Arc flash labels are yet another manner to advise people about the dangers in a particular area. You can get ones that inform employees about the location of the danger, the temperatures involved or the measures they need to take. You can find arc flash warning labels in lots of stores, both online and physical, and their prices start at $13,79. Remember that there are also some arc flash label requirements you need to consult before getting some.
Arc Flash Injuries and How to Apply First Aid
When talking about injuries, we have to keep in mind that the arc flash temperatures reach more than 35,000 °F or 19,400 °C at the terminals. This means that the massive amount of energy that is released in the arc fault will vaporize the metal conductors it finds in its way, it will melt and blast the metal and it will expand the plasma outward. This translates to destroying the equipment, triggering fires and injuring the electrical workers, as well as any bystander.
Severe burns are the most common injury that appears in such circumstances. They are caused by the intense heat, which triggers the ignition of the clothing. Treating the arc flash burns is a very complicated and difficult process involving years of skin grafts. Among the other injuries that can happen, we must take note of:
- Eye damage, caused by molten debris and projectiles (in case of a lack of proper eye protection);
- Retina damage, done by the intense UV radiation in the moment of the flash;
- Lung damage, produced by the superheating of the vapors;
- Hearing affections, such as eardrums ruptured by the thermoacoustic blast;
- Broken bones and other injuries, which appear when the victim is knocked off their feet.
The vapors superheat and can permanently affect the lungs, thus impairing breathing. Hearing is also affected because of the thermoacoustic blast. People have often been reported to have ruptured eardrums after suffering such an incident. The blast is so powerful that it knocks people off their feet, which then again may result in electrocution, broken bones or other injuries
Minimal First Aid in Case of Injury
When it comes to offering first aid, every second matters. Usually, the victim is suffering severe burns, case in which there are four critical steps that need to be followed:
- Stopping the burning process – take the victim away from the circuit by using non-conductive material. Smother or douse the fire on the victim and remove any smoldering clothing.
- Cooling the burn – run cool water (not cold!) over the burn.
- Offering pain relief – if you don’t have a medical expertise, it’s better not to give the victim any pills. If they are conscious, you can talk to them and explain what happened until help arrives.
- Covering and protecting the burn area so as not to be contaminated – use a clean dry cloth for this and apply it only after the burn has been cooled. Do not use any ice, creams or other ointments!
You can get a standard emergency burn arc flash kit in case of emergency. However, despite this, specialized medical help is necessary as soon as possible, so make sure you provide it if you tend to an arc flash explosions victim.
An arc flash accident is not as rare as we would want it to be. They can be triggered in an instant and the consequences can be huge. For this reason, it is important to be informed and prepared for any event. All companies should have adequate PPE (personal protective equipment). They should try as much as they can to reduce the risk of such explosions happening. Finally, assessing the risk in a correct manner and warning all the employees about it can prove to be essential when talking about saving lives.