It is good to hear that this blog is getting those involved with electrical safety to think and talk about what they are doing to protect employees from electrical injury. I have been asked to explain what it means to use the hierarchy of risk controls regardless of a policy requiring the establishment of an electrically safe work condition (ESWC) or permitting justified energized work. How to use the hierarchy is obvious when it comes to justified energized work. However, using the hierarchy when establishing an ESWC is less obvious to many. It should be used the same way regardless of your policy. This comes down to considering the act of establishing an ESWC to be an administrative control to achieve elimination of the hazard. Bear with me and hopefully this will again shed some light on the process. Remember that the act of establishing an ESWC is considered to be energized work.
Consider an electrical installation with a step-up transformer (480/2400 volts) being used for a motor installation. An interrupting switch for a motor load is on the secondary. The primary disconnect and overcurrent device is located back at the switchgear. The incident energy at the transformer input terminal is 22 cal/cm2 with an arc-flash boundary out at 12 feet. Your employee will don 25 cal/cm2 PPE. This will require a full hood and arc-rated gloves. She will complete the eight steps in 120.5. She interrupts the motor circuit then opens the breaker in the switchgear. She goes into the transformer enclosure to verify the absence of voltage. The limited approach boundary is at 5 feet because the secondary is exposed. She is within the restricted approach boundary (2 feet, 2 inches) of the secondary terminals which requires the use of insulated tools and shock PPE rated for 2,400 volts. She will have established an ESWC while being potentially subjected to 2,400 volts and 22 cal/cm2.
If the hierarchy of risk controls was used, here is what the scenario might have been when establishing this EWSC. The overcurrent device is replaced with a current-limiting device with a faster clearing time to lower the incident energy to 8 cal/cm2. The arc-flash boundary has been lowered to 5 feet. There is a viewing window in the motor disconnect to permit visual verification that the load has been isolated. (Yes, this not the disconnect device but it is still used here.) The switchgear is arc-rated so that if an incident occurs when opening the breaker the arc-flash will be directed away from the employee. The input terminals of the transformer are in a separate enclosure allowing the use of shock PPE rated for 480 volts. The limited approach boundary is now at 3 feet 6 inches and the restricted approach boundary is 1 foot. The employee dons 10 cal/cm2 PPE with leather glove protectors and a face shield. She will complete the eight steps of 120.5. She verifies that the contacts isolating the motor load are clear. She opens the breaker in the switchgear then opens the transformer terminal box to verify the absence of voltage. She has also established an ESWC while potentially being subjected to 480 volts and 8 cal/cm2. Other methods might have been used to mitigate the hazard. The point is the hierarchy of risk controls was used to increase safety for the employee rather than solely establishing an ESWC.
Your employee can be injured at 480 volts and 8 cal/cm2 just as she can be injured at 2,400 volts and 22 cal/cm2. However, there is less risk and lower hazard levels in the second scenario. This is why you must consider the hierarchy even when your policy is to establish an ESWC. You may decide not to use some or all other controls but your risk assessment should consider them. There should never be energy present and the voltage measured should always be zero when an ESWC is being properly established. Your employee should truly never be exposed to an electrical hazard.
So why go through these additional steps? I am aware of situations where equipment is labeled with an incident energy higher than what currently available PPE is rated to provide protection from. The apparent “theory” is that since the policy is to eliminate the hazard through an ESWC that the hierarchy need not be used to lower the risk or hazard. Using and wearing inadequately rated PPE might be considered by many to be as irresponsible as not using any PPE. The personal protection your employee is required to use is for no other reason than something unexpected might happen that could injure them. When that does happen isn’t it important to provide, if not at least consider, a higher level of protection for that employee?
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For more information on NFPA 70E, Standard for Electrical Safety in the Workplace, read my entire NFPA 70E blog series on Xchange
Next time: NFPA 70E First Draft Meeting