OHS professionals are educated to identify workplace hazards, assess the risk associated with those hazards and implement effective risk control by applying a hierarchy of risk control measures. However, in many cases they receive little, if any, education regarding the most ubiquitous form of toxic energy: electricity. All too often, safety professionals leave electrical safety to the electrical professionals, believing those individuals are the “experts.”
On the other hand, electrical professionals would have significant education and experience on electrical installations, but that education typically does not include OHS theory and practice.
Electrical safety can be advanced through a co-operative effort between the two professions using OHS risk management principles.
Risk management process
The purpose of the iterative risk management process (Figure 1) is to identify hazards, assess the risk deriving from those hazards and identify and implement risk controls, either alone or in combination, to achieve a level of risk that is “as low as reasonably practicable” (ALARP).
Using definitions under CSA Z1002, a “hazard” is a potential source of harm to a worker, while “risk” is the combination of the likelihood of the occurrence of harm and the severity of that harm. We will focus on the aspect of identifying risk criteria when establishing the context, and applying risk assessment and risk control methods to electrical hazards.
Employers are required by law to exercise due diligence and create a workplace free of reasonably foreseeable harm. Shock and arc flash injuries are a reasonably foreseeable harm.
There are now many technological solutions for each risk control method in the hierarchy of risk controls that, when used individually or in combination, facilitate the avoidance of harm from electrical hazards.
The risk associated with electrical hazards can be managed by applying the hierarchy of risk controls to achieve a level of risk that is ALARP.
Risk analysis for electric shock
The likelihood of occurrence of a shock incident relates to whether an electrical conductor is exposed; and whether or not a person is closer than a “safe” distance. CSA Z462-12 defines the “safe” distance as the “limited approach boundary.”
The severity of the effect of electricity on human tissue correlates to the amount of electric current flowing through the tissue and duration of the current flow. According to Ohms Law, the flow of electric current is a function of the voltage applied. Therefore, to a limited degree, the severity of an electric shock incident can be correlated to the level of voltage. CSA Z462-12 clause 126.96.36.199 indicates the threshold below which voltage would not be considered hazardous is 30 Vac (rms) and 60 Vdc.
Risk analysis for arc flash
The likelihood of an arc flash incident correlates to the likelihood that the insulation or isolation of an energized conductor can be compromised. Factors affecting this likelihood can be grouped into two broad, but interrelated categories: activities or tasks that involve interacting with energized electrical equipment; and, the condition of the electrical equipment.
CSA Z462 describes some interactions with electrical equipment as normal — that is, they have a likelihood that is ALARP of initiating an arc flash incident. An example of a normal interaction is the operation of a circuit breaker or fused switch with the enclosure door closed.
CSA Z462 describes the condition of electrical equipment as normal if it is properly installed and properly maintained. Codes and standards should be used to determine if equipment is properly installed and maintained. Factors affecting equipment condition include the application, the state of the equipment (for example, doors closed and covers in place), the state of maintenance, the frequency of operation and the environment the equipment is located in.
If both the planned activity and the equipment condition can be characterized as normal, then the likelihood an arc flash event might occur can be described as ALARP.
In occupational health and safety, severity of harm is usually proportional to the dose or magnitude of exposure. In arc flash terms, the magnitude of thermal exposure is called incident energy. Incident energy is an estimate of the thermal energy density (in calories/cm2) that could occur at a specific distance from the electric arc. The distance is the linear distance from the electric arc to the expected location of a worker’s torso, typically 18 inches for electrical equipment rated less than 750 volts.
There is considerable controversy over whether there is an acceptable level of incident energy exposure. Standards such as CSA Z462 imply incident energy exposures up to the point of causing second-degree skin burn are acceptable. When applying risk management principles, this author does not accept the premise there is an acceptable level of incident energy exposure.
Risk analysis includes risk estimation. The level of the risk for either shock or arc flash is estimated by combining likelihood and severity. When either likelihood or severity is ALARP, the level of risk is ALARP. If both likelihood and severity are not ALARP, then the level of risk is not ALARP.
Risk evaluation compares the estimated level of risk to the risk criteria. The risk criteria established in this article is to achieve a level of risk that is ALARP by applying the hierarchy of risk controls to electrical hazards. When the level of risk is ALARP then risk controls do not need to be applied as harm is not reasonably foreseeable. When the estimated level of risk is not ALARP then risk controls need to be applied individually or in combination to achieve a level of risk that is ALARP.
The following is not an exhaustive list, but is intended to illustrate how the hierarchy of controls might be applied to electrical hazards.
Elimination: Creating a zero energy state, or de-energizing, is the most important risk control method for electrical hazards. Unfortunately, it is also the risk control method most often overlooked by the electrical professional in many industrial, construction and commercial settings. It’s vital to note some of the steps involved in de-energizing have some attendant risks. For example, when testing for the absence of voltage to verify a zero energy state, there is likelihood of exposure to both electric shock and arc flash.
Substitution: The likelihood of electric shock can be reduced by substituting 120 vac electrical distribution system controls with 24 vac controls. The likelihood of an arc flash incident occurring can be reduced by substituting a solidly grounded electrical distribution system with high-resistance grounded system (when technically feasible). According to one study, single-phase ground fault incidents represent about 98 per cent of all electrical distribution system failures.
Engineering controls: The likelihood of electric shock can be reduced by guarding routinely accessed areas of electrical equipment to prevent inadvertent access to energized conductors, and by using “finger safe” components. Incident energy exposure can be reduced or eliminated by creating distance between the worker and the arc flash energy through remote operation. The potential severity of an arc flash incident can be reduced by using faster fault clearing devices (fuses or circuit breakers).
Systems: Increasing awareness of potential hazards can include the use of signage to indicate the presence of a hazard, and the potential severity of exposure to that hazard.
Administrative controls: These include commission testing a new installation to ensure the equipment is installed per the manufacturer’s specifications and applicable codes and standards, and adequate maintenance and repair activities. Improper or inadequate maintenance of electrical distribution equipment will have the effect of increasing the likelihood and the potential severity of an arc flash incident.
Personal protective equipment (PPE): When the other control methods fail to achieve a level of risk that is ALARP, then PPE is utilized as a last resort. It is important to note PPE is a risk control option for severity of exposure, not likelihood of exposure. PPE performance rating must meet or exceed the estimated severity of exposure. Whether or not PPE is required in a given work situation would be the result of estimating the likelihood of exposure.
Taking safety performance to the next level requires joint effort between electrical professionals and safety professionals. Using common language and processes of risk management will facilitate this.
Risk management principles and processes can be applied at any stage in the lifecycle of the electrical distribution equipment. Applying the risk management process to electrical hazards ensures risk control methods are identified and applied in a hierarchical approach. Because it is an iterative process, applying risk management will ensure continuous improvement in managing electrical risks.
Daniel Roberts is the national safety manager for Schneider Electric Canada Services and Projects. He can be reached at firstname.lastname@example.org[/em]