Engineering Methods of Hazard Reduction & Mitigation

Many safety leaders have stated that they do not allow qualified employees to work on or near exposed live (energized) circuits.  They have created a policy that all energized circuit shall be de-energized and locked and tagged (LOTO) per specific control of hazardous energy policies.  This is a great policy, but it is not always feasible.

There are some systems that cannot be easily de-energized.  OSHA's requirement for working on energized equipment is “Live parts to which an employee may be exposed shall be deenergized before the employee works on or near them, unless the employer can demonstrate that deenergizing introduces additional or increased hazards or is infeasible due to equipment design or operational limitations” [OSHA 29 CFR 1910.333(a)(1)]. 

Electrical systems that are identified as emergency systems (NFPA 70, Chapter 700), legally required systems (NFPA 70, Chapter 701), and critical operating power systems (NFPA 70, Chapter 708) cannot be de-energized unless permission is obtained from the appropriate governmental authority have jurisdiction (AHJ).  Emergency power systems are critical for life safety and include many healthcare facilities.  Emergency power systems are also located in every public building and include emergency lighting for egress and fire suppression, alarm, and communication circuits.  Legally required power systems include those systems that if de-energized, can create a greater hazard to the community.  Legally required power systems include those systems that control pollution abatement systems, chemical containment systems, and the like.  Critical operating power systems include those systems that critical to functionality of the US.  This includes water, transportation, energy, transportation, and specific monetary functions.

Another type of power system is the optional power systems (NFPA 70, Chapter 702).  Optional (nonessential) power systems are those systems and loads that are related to business continuity.  These power systems can be de-energized without creating safety hazards, although they may impact the business.  

In addition to systems that cannot be de-energized easily because of legal requirements, specific activities such as troubleshooting, testing and measuring of voltage, current, power or related parameters must be conducted when electrical equipment is energized on all types of power systems [NFPA 70E-2015, Chapter 130].  There are other activities that may also require qualified personnel to interact with exposed live (energized) circuits.  This includes the adjustment and programming of equipment.  These activities can be conducted on all types of electrical systems and in locations such as manufacturing environments, R&D laboratories, production testing environments, and many more.

Last month’s blog focused on the Administrative Methods of hazard reduction and mitigation of electrical hazards.  While administrative methods can be effective, they also present an opportunity for injuries to occur.  Hazard reduction and mitigation techniques are more reliable and effective when Engineering Methods are implemented.

The Engineering Methods of hazard reduction and mitigation of electrical hazards include:

• ·         Elimination
• ·         Substitution
• ·         Guarding
• ·         Safety Control Systems

Guarding of electrical hazards are what is accomplished by equipment enclosures.  Enclosures protect all people who are in close proximity to the equipment from interacting with the equipment.  However, when qualified employees need to conduct troubleshooting or testing, they need to have access to the exposed live (energized) circuits.

Safety control systems are typically devoted to keep employees out of a hazardous area and can be very loosely similar to guarding principles.  Common equipment associated with safety control systems include using light-curtains, pressure mats, interlocks, or other components tied into a safety rated programmable logic controller (PLC).

The substitution principle can be used by changing the operating voltage that the qualified employee is required to interact with.  This includes changing control voltages from 120V or 240V to 24V.  The 24V control circuit can be located in a separate cabinet that is isolated from any circuit that is 50V or greater.  Qualified employees working on system voltages of 24V are generally not exposed to shock or arc flash hazards.

To eliminate electrical hazards, designers and engineers can remove the need for people to interact with exposed live (energized) circuits.  This includes designing equipment such that user interface equipment is located on the front panel of the equipment.  Examples include using HMI’s, remote panels for SCRs or other industrial control components, remote communication interface ports, etc.  Eliminating qualified personnel from interacting with exposed live (energized) circuits can be achieved on new equipment that is in the design phase, but is not very practical for equipment that is already installed.

As the term Engineering Methods suggests, engineering activities are required to assess the risks of the activities, and to reduce or mitigate the hazards.  For qualified employees working on exposed live (energized) circuits, the implementation of engineering methods to reduce or mitigate arc flash hazards will result in a safer workplace.