Data Center Electrical Safety
Arc-flash hazard warning label
Electrical shock and arc flash are the two primary types of electrical safety hazard in your workplace.
Electrical shock occurs when the human body becomes part of an energized electrical circuit. The degree of injury is directly related to the path the current takes through the body. As little as one milliamp is enough to cause death.
Arc flash is literally a fireball that occurs when an energized conductor is unintentionally connected to another energized conductor or ground. The air within the sphere of the established arc becomes conductive and the arc grows exponentially until such time as current is interrupted.
Question: What is an arc-flash hazard warning label?
Answer: A label containing all necessary information about the arc-flash hazard faced at a specific location that is affixed to each piece of electrical equipment with a removable cover or door providing access to current carrying conductors when energized (see the figure).
Question: What information is contained on the arc-flash hazard warning label?
Answer: All pertinent information necessary so personnel understand the degree of hazard faced and protective measures required.
• Hazard class: the level of hazard exposure.
• Incident energy: the amount of energy generated during an electrical arc impressed on a surface, 18 in. (the length of the average forearm) away from the source of the arc expressed in calories per centimeter squared (cal/cm²). This is worst case as if you were standing directly in front of the energized conductor. The farther you are from the source, the lower the cal/cm².
• Personal protective equipment (PPE) required: the specific PPE required for the class hazard faced.
• Voltage hazard: the voltage level one would be exposed to at the point of access.
• Equipment identification: the equipment the information refers to.
• Arc flash protection boundary: the distance from the access point at which the incident energy from an arcing fault falling would equal 1.2 cal/cm² (equivalent to a mild sunburn).
• Limited approach boundary: the line that may not be crossed by unqualified persons, unless accompanied by qualified persons both wearing appropriate PPE.
• Restricted approach boundary: the boundary that only qualified persons are permitted to approach exposed, energized conductors, wearing appropriate PPE and with a written and approved work plan.
• Prohibited approach boundary: the line that is considered to be the same as actually contacting the exposed part. A risk assessment must be completed prior to crossing this line.
Question:How do manufacturers deal with this hazard when designing electrical gear?
Answer: Manufacturers are promoting a variety of design features generally divided into active and passive solutions. Active protection seeks to prevent the arc from happening and mitigating the event to a high degree. Examples include:
• Arc-flash detection. Since an arc flash will continue until current is interrupted, early detection is a huge advantage. One such detector incorporates an unclad fiberoptic loop routed around the inside of the gear to detect a sudden change in the intensity of the ambient light over a very brief duration of time coupled with current transformers to detect the current spike associated with an arc-flash incident. The output of this detector is designed to trip the upstream over current device very quickly thereby minimizing the duration of the event.
• Some manufacturers have taken a more direct physical approach by coupling rapid detection of an arc-flash event with the direct physical intervention of a secondary fault, which is designed to safely deplete the energy from the original fault and trip the upstream over current protective device. One such device is GE’s Arc Vault. This device is connected directly to the bus and after detecting an arc flash, strikes a plasma arc inside a robust container thereby sapping the energy from the uncontrolled arc flash and effectively extinguishing the destructive arc flash.
Passive protection is mainly provided in what is being termed “fault tolerant” design. This means that gear is designed to minimize damage and physically withstand an arc flash. Common mechanical design features include louvers in the top to relieve the tremendous pressure created by an arc-flash event, ducts or chutes to direct the arc up and out, and reinforced cover and doors, etc. While this approach is desirable, it is reactive. Regardless of these features, an arc flash creates real direct and collateral damage that must be repaired. It is a bit like insurance, the building burned, we lost everything, but we got a check. Arc-flash incidents result in damage and interruption of business operations.
Examples of passive solutions are:
• Remote-controlled circuit breaker draw out machines. This device is designed primarily to protect the operator in case of a malfunction during service work.
• Service setting on controls and over current protective devises temporarily set relays and trip devices to minimum levels during service and repair activities again in order to rapidly trip the relay or device and interrupt fault current extinguishing the arc flash.
Electrical safety is not an option. This topic is broad and complex and requires the allocation of significant resources to establish a comprehensive program. Four to five injuries or deaths occur each day in the U.S. as a result of electrical shock or arc flash. You can debate the difference between standards and statutes; however, standards are the basis for statutes and codes.
One industry study concludes the minimum cost of an arc-flash event is $750,000. I would submit that it is likely to be a lot higher when you consider the direct damage to the equipment and facility, the liability as a result of injury or death, and the business disruption. As a facility manager, you could be held personally liable in the event of an incident if you fail to enforce safe work practices for your employees and contractors. In a court of law or the court of public opinion, you’ll fare much better having done the right thing. It’s time to get serious about electrical safety in every facility. Protect your employees, your contractors, and your company.