Understanding The Arc Flash Danger: How Bad Could It Be?
By Derek Vigstol, Contributor
The importance of the risk assessment method used takes a back seat to the reality that a labeled work environment is a safer environment with respect to arc flash because it removes the pressure to accurately assess the arc flash risk on the fly.
It’s no secret that arc flash and arc blast are real hazards that present themselves when working with and around electrical equipment. And with regulations, such as OSHA, mandating that workplaces be free from known and recognized hazards, we all have a responsibility to do everything we can to mitigate the risk of injury to employees from arc flash/blast. However, if we are going to protect individuals from the hazards, we might want to have an accurate idea of just what those hazards entail. This means having a rock-solid understanding of the arc flash risk assessment process to determine which strategy is needed to protect the worker.
Let’s start by looking at what the risk assessment process is supposed to provide. During the risk assessment procedure, our main goals are to determine if the employee is exposed to a hazard during the course of the task at hand, determine what risk level the employee is exposed to, and then determine what they are going to do about it to stay safe. With risk being defined as the combination of how likely an injury is to occur and the possible severity of said injury should it occur; we see the structure of the risk assessment process start to take shape. Basically, we must ask ourselves, “Is what we are about to go do likely to cause an arc flash and, if so, how bad is it going to be?”
Industry seems to have a pretty good handle on estimating how likely an arc flash is to occur; however, when it comes to estimating the severity, there seems to be a bit of an issue as to what needs to be done. NFPA 70E®: Standard for Electrical Safety in the Workplace® points us to two options for estimating the severity of an arc flash: Incident Energy Analysis (IEA) and The PPE Category Method. Either of these methods can be used to provide the needed information for the selection of PPE employees must wear to protect themselves when the risk has not been lowered to a satisfactory level by other means within the hierarchy of risk control methods, such as hazard elimination or engineering controls. However, if you are like this author and a stickler for the details, there is one clear winner when it comes to accuracy in estimating the severity of an arc flash, and that is the incident energy analysis.
The Incident Energy Analysis
IEA involves a full-on study of the equipment in the system, the available energy during fault conditions, and calculates the amount of thermal energy released based on the estimate of what the arcing current might be at that point in the system and how long the arcing fault will be allowed to persist based on the clearing time of the upstream overcurrent protective device. This study will also estimate where the arc flash boundary needs to be established, which is the distance at which the incident energy equals 1.2 calories per square centimeter. However, the downside to this method is that if it has not been performed prior to the work being performed, it isn’t very realistic to quickly whip out an incident energy analysis as the employee is standing in front of the equipment ready to go to work. That is where the PPE Category Method becomes important.
The PPE Category Method
Performing an arc flash study or incident energy analysis also often leads to the equipment being labeled with the results of the study. This is a huge benefit to those exposed to the arc flash hazard because the results of the risk assessment are pre-populated at the point of work or close by. This isn’t to say that a label can’t be made using the PPE Category Method, because it absolutely can be used for the label information, but it is the experience of this author that facilities with an IEA performed tend to have a higher probability of having these labels installed. This is optimal for employees who must wear PPE to mitigate the risk as they simply need to select arc-rated PPE that exceeds the value on the label for any body part that will cross the arc flash boundary. There is also a table in NFPA 70E® that gives guidance as to what articles of PPE this entails based on the severity of the hazard, Table 130.5(G).
Understanding exactly how to apply the PPE Category Method becomes a bit more confusing than when an IEA has been performed. However, it has served as a useful tool for employees without the benefit of access to the results of an IEA. Simply put, the PPE Category Method is an attempt to categorize equipment by equipment type, amount of available fault current, and the type of upstream overcurrent protective device that will be interrupting the fault should one occur. It is more of a situational response or a sort of, “If you have a panelboard connected to a system capable of supplying no more than this many amps for this amount of time, then this level of PPE should reduce the severity of injury to a survivable level” kind of approach. Not super accurate on understanding the exact risk, but it is better than not doing anything at all. Let’s face it, people rarely are injured or killed because they aren’t wearing enough arc-rated PPE; they are injured or killed when they aren’t wearing any PPE at all.
Whichever method is utilized, it becomes more important that we stress how beneficial it can be for the protection of employees to have this information provided beforehand. The importance of the method used takes a back seat to the reality that a labeled work environment is a safer environment with respect to arc flash because it removes the pressure to accurately assess the arc flash risk on the fly. Employees that must make heads or tails of this process are doing so while also juggling pressure from several other influences. Providing a labeled environment simplifies the process for those affected and reduces the potential impact of human error. Failing to take this crucial step is failing to provide employees with a workplace where every effort has been made to protect them from the hazard of arc flash. ESW
Derek Vigstol is an electrical safety consultant for E-Hazard and co-host of E-Hazard’s electrical safety podcast, “Plugged Into Safety.” E-Hazard is the industry leading provider of electrical safety consulting & training services (www.e-hazard.com).