Electrical systems have posed hazards since they were introduced more than 100 years ago. Although evaluating these hazards and identifying the appropriate personal protective equipment (PPE) is a major task of electrical safety programs, the risk associated with the hazards is frequently overlooked.
It’s more than just the hazard
According to the National Fire Protection Association’s 2015 edition of NFPA 70E, a risk assessment is required. In the past, one had to determine the severity of the hazard and the appropriate PPE level. It now includes assessing the risk and risk control.
The 2015 edition of NFPA 70E defines risk as “a combination of the likelihood of occurrence of injury or damage to health and the severity of injury or damage to health that results from a hazard.” Notice the words “likelihood” and “severity” in the definition.
The hierarchy of risk control methods specified in ANSI/AIHA Z10, American National Standard for Occupation Health and Safety Management Systems, is as follows:
- Engineering controls
- Administrative controls
- Personal protective equipment (PPE)
Method No. 1, elimination, has been at the heart of electrical safety programs, and NFPA 70E requires establishing an electrically safe working condition, with a few exceptions. Elimination of the hazard when possible is always the best approach. Method No. 6, PPE, is also a critical component of electrical safety programs. However, notice it is last in the hierarchy. There are four other risk-control methods between elimination and PPE.
IEEE 1814, Safety by Design and Risk Control
The Institute of Electrical and Electronics Engineers (IEEE) created a working group several years ago with the task of developing a new standard known as “IEEE 1814—Recommended Practice for Electrical System Design Techniques to Improve Electrical Safety.” The standard is getting closer to completion. When published, it will provide guidance for integrating more safety elements into the design of electric-power systems.
According to the latest draft of this proposed standard, the scope is as follows: “This Recommended Practice addresses system and equipment design techniques and equipment selection that will improve electrical safety. The techniques in this Practice are intended to supplement the minimum requirements of installation codes and equipment standards.”
Topping out at nearly 100 pages (so far), many of the design practices outlined in IEEE 1814TM can help control and reduce the risk associated with electrical hazards. The new standard will provide a wealth of information. Here is a sample of topics that it covers.
The National Electrical Code (NEC) defines the minimum requirements for properly selecting overcurrent protective devices. This new standard looks deeper at topics such as differences between current-limiting and noncurrent-limiting devices as well as the device’s instantaneous trip setting and the effect on the arc flash hazard. Make the wrong selection and the arc flash hazard could become more severe even though you complied with the NEC.
Maintenance and operation also need to be considered. During the design stage, an initial risk assessment should be conducted to identify important safety details, such as where energy isolation devices are needed.
Facilities with a 24/7 continuous or uninterruptible operation should factor in redundancy. The new standard discusses various design options in great detail.
Distance is another factor when it comes to arc flash safety. The closer a person is to an arc flash, the greater the incident-energy exposure. The electrical design should also consider the use of remote-operated devices to keep workers out of harm’s way.
Selective coordination requires protective devices to be selected and/or set so only the device nearest the fault interrupts and the other devices remain closed. This minimizes the extent of an outage and typically requires a protective device closer to the source to operate more slowly than devices closer to the load in response to abnormal currents. However, the slower response needed for selectivity contradicts the need for faster response to reduce an arc flash’s incident energy.
There are many methods that can be used to provide the best of both worlds. Arc flash energy-reduction methods, such as maintenance switches and devices with multiple setting groups, can be used to temporarily enable high-speed fault clearing when an arc flash hazard is present. Differential protection and zone-selective interlocking may also be used.
This is just the tip of IEEE 1814’s iceberg. The introduction of risk assessment and risk control in the 2015 edition of NFPA 70E is a game-changer. IEEE 1814 will go a long way toward helping the electrical designer meet these new requirements by controlling risk through safer design.