Accidents involving personnel performing work on energized electrical equipment have been occurring ever since electricity was first generated and distributed for industrial applications. Recent changes to standards like NFPA 70E 2004/Standard for Electrical Safety in the Workplace and the National Electric Code (NFPA 70 2005), along with enforcement of these standards by OSHA, are radically changing the way that workers and their employers manage tasks involving energized electrical equipment.
The standards cover all hazards to personnel when they are working on energized electrical equipment, which include shock, electrocution, arc flash, and arc blast. While most electrical workers are, and historically have been, reasonably well aware of the shock hazard when working on energized electrical equipment, very few implicitly understand the potential consequences of the arc flash and blast hazards, and how to protect themselves. (Photo courtesy of Fluke Corp.)
Arc flash accidents that result in a fatality or serious hospitalized injury occur 5-10 times every day in the United States, for example. If a worker survives an arc flash accident, he or she often sustains life-altering, permanently disabling injuries. Typically, the final cost to employers and their insurers for a single serious, but survived, accident will approach $10 million, including litigation fees, fines, equipment damage, business interruption, and elevated insurance premium rates.
Important work has been done by electrical equipment manufacturers and NFPA in recent years to better understand the dynamics of arc flash accidents, and to develop methods and formulas to calculate the potential arc flash hazard to workers during these events. These efforts are already making a significant contribution to reducing the accident rate by educating workers, defining processes, providing Personal Protective Equipment (PPE) and safety tools, and developing internal safety programs that will help keep electrical workers safe.
Training Is Crucial
Arcing faults in electrical equipment can occur in several different ways. Sometimes these events can occur spontaneously, as a result of poor maintenance, dirty environmental conditions, or mechanical failure. Many documented cases of arcing faults were caused by rodents or other small animals entering the equipment and compromising the insulation distance between electrically energized parts. These events, however, are fairly rare, and when they do occur, typically result in equipment damage but not worker injury, because the worker is not usually near the equipment when the arcing fault occurs.
The latest standards make it very clear that the fundamental safety requirement is to de-energize electrical equipment before personnel work on or near it. There are exceptions to this requirement to de-energize, but the exceptions are only permitted in very clearly defined circumstances, and in those cases, require the work to be well planned, authorized, and documented. The process of de-energizing electrical equipment is usually called Lock Out Tag Out (LOTO); a number of documented steps are required to do it safely.
The largest majority of arcing faults involve a mistake made by personnel when performing work on energized electrical equipment. A post-accident analysis of these events usually reveals that in the greatest majority of cases, the arcing fault was initiated by the worker. These cases usually result from some unsafe work practice -- and unsafe work practices usually equate to a lack of training.
NFPA 70E 2004 (Article 100, Definitions) defines a qualified person as "one who has skills and knowledge related to the construction and operation of the electrical equipment and installations and has received safety training on the hazards involved." This training requirement applies to all electrical workers, regardless of their prior qualifications, skill, or experience level. The worker training must cover all hazards, including shock and electrocution in addition to arc flash and arc blast. This required electrical safety training is available from many sources, and is a critical first step in protecting workers from harm.
Complying with these new safety standards can be a costly, lengthy, and demanding process for most employers. Electrical safety training, while only one of the requirements, can be done quickly, with minimal cost. And of all of the safety compliance requirements in the standards, the requirement for safety training can potentially have the largest and most immediate impact on the accident rate, by educating workers on the hazards, and teaching them how to avoid them.
Worker Responsibility
Workers get hurt for one of two reasons: they either did something they knew could cause injury or death, thinking it wouldn't happen to them; or they did not know that what they were about to do could result in injury or death. One statement heard frequently after an occurrence is, "I thought . . ." It bears mentioning that it doesn't matter what follows those words when working with a force that can cause the immediate demise of the worker as a result of any accidental contact. In such a case, any explanation that begins with "I thought . . ." is unacceptable.
Workers not only need to know, but must be absolutely sure, that what they do is the safest procedure to accomplish a given task. For this reason, workers need to be trained to recognize hazards specific to the equipment and the task to be performed under specific circumstances. For the simple fact is, all electrically related occurrences are preventable. For an injury to occur, the employee must perform an unsafe act. Following are two examples of common tasks involving electrical equipment, well-known procedures for addressing each issue, and safer alternatives.
Example 1: Line voltage to test a fuse
A commonly used procedure for the simple task of determining which fuse is blown in a 480 V disconnect is as follows:
- Turn off the disconnect.
- Defeat the door interlock.
- Turn the switch back on.
- Take voltage readings across the fuse or in a three-phase application from the line side of the disconnect to the load side of the fuse on another phase.
The worker is trying to determine what, if anything, is wrong with the equipment. Electrical equipment is most dangerous when something is wrong with it. Hence, the worker needs to spend as little time as possible in proximity to energized electrical equipment with the door open and/or cover removed.
The test above is dangerous for a number of reasons:
- It exposes the employee to two major hazards -- electrocution and arc flash.
- Applying a meter across an open fuse could cause the connected equipment to start unexpectedly.
- If the problem is not a blown fuse, the employee just closed the disconnect with the door open.
- There is also the possibility of installing a new replacement fuse into an energized circuit, which is a dangerous practice.
A safer procedure would begin with opening the disconnect and leaving it open, then verifying there is no voltage present at the line side or load side of the fuses. The worker should then use an ohmmeter or continuity tester to check the fuses. Why use 480 V to test a fuse when 9 V (essentially a meter battery) will accomplish the same thing? Some years ago, an electrician and four other people died in a fire when the electrician installed a fuse in an energized disconnect. By all indications, the fuses in the disconnect were tested using the line voltage. However, the electrician didn't realize it was energized when he attempted to install the new fuse. One effective way to prevent this unsafe practice from happening is to establish a policy and procedure that testing a fuse with a line voltage will result in immediate disciplinary action or termination of employment.
Example 2: Voltage drop/Watts's loss test
An electrical worker suspects high-contact resistance in a starter connection is responsible for nuisance tripping of the overload relay or fuse blowing. A common unsafe procedure involves using a voltmeter across the contacts to measure the voltage drop. Higher voltage measured equates to higher resistance at the point of connection. This high resistance generates heat, resulting in blown fuses and/or overload relay operations. Once again, we find the employee standing in front of equipment that is energized and under load.
A substantially safer way to evaluate connections in electrical equipment is to use a low-resistance ohmmeter on de-energized equipment. For $100, a noncontact temperature probe could be purchased and used with the proper PPE to detect abnormal heating generated by high contact resistance at fuse, breaker, or starter connections and/or contacts. This test is not as safe as using a low-resistance ohmmeter on a de-energized circuit, but is an alternative that increases the distance between the worker and the equipment and does not require disturbing energized parts.
Safety Program vs Safety Culture
A safety program requires monitoring employees for compliance with safety rules. But when a company establishes a safety culture, personnel tend to adhere to the resultant safe work practices because they believe working safely is the right thing to do. A safety culture empowers workers to modify existing rules and, if necessary, create new rules in the interest of safety. An effective safety culture begins at the top -- management leads the effort to assure the safety of all employees. A commitment to provide tools, PPE, and training demonstrates to all personnel that safety is the top priority. Establishing a safety culture also empowers workers to assess a situation and determine how to proceed . . . or whether to proceed at all, based on the equipment and circumstances.
Safety is an ethical responsibility to protect workers by any means necessary.
In order to keep critical systems operating, training is essential. Companies staffed with personnel trained in the proper procedures regarding equipment operation and safety minimize occurrences and downtime. In light of the more than 10,000 electrical accidents that occur each year, resulting in numerous serious injuries from which some never recover sufficiently to work again, training saves time, money, and lives.
To learn more about arc flash, click here.
