The term “life cycle safety” simply refers to the electrical safety factors that must be considered for the life of a piece of equipment or system. Such safety considerations begin at the initial design stages of a project. Although design cannot eliminate unsafe acts by irresponsible employees, it can incorporate measures to reduce the individual's ability to take a risk.
One of the biggest challenges to life cycle safety is cost. The Figure (click here to see Figure) illustrates the cost influence curve, which shows that influences to overall project/system safety considerations have more of an impact and cost less when factored into the mix early on. Using this cost influence curve concept allows designers to minimize cost impact while positively influencing the safety considerations and implementations to systems and projects.
Cutting too many costs at the design level, however, can compromise workers' safety and result in long-term economic losses associated with system downtime, on-site design repairs, and injury to workers that may result in legal action. Obviously, cutting too many corners can be more costly and unsafe than if the original budget had provided sufficient funding for life cycle safety.
The safe design of an electrical system begins with the design engineers. Although they must consider many topics in the course of their work, they should never lose sight of the following areas of overall safety.
Accessibility of control is paramount. In particular, stop buttons and stop cords must be readily accessible. An operator should neither have to travel nor reach any extended distance to activate a stop button, especially an emergency stop function.
Arrangement of controls and displays should be oriented so that the operator can easily interpret the information.
Identification of devices should be standardized and included in the safety design reviews. Proper labeling and color coding, as well as shape and location of control devices, are an important consideration for rapid, reliable, and safe response.
Component selection should take ergonomics into account.
Adequate working space and illumination inside of cabinets must be considered. For example, maintenance personnel must be provided with proper lighting and safe access for voltage testing within the enclosure.
The arrangement of components within an enclosure can also improve safety. A few considerations are locating, monitoring, and adjustment devices for easy access and physically locating commonly tested equipment at a convenient height.
A fail-safe design may be identified as one in which failure of a wire, circuit component, or energy source will not cause an accident or process upset. The fail-safe design should consider all prime energy sources by the electrical, pneumatic, and/or hydraulic systems.
Adequate spacing and illumination
The NEC establishes the minimum required guidelines for the working space in front of electrical equipment in Table 110.26(A)(1) and 110.34(A) for various conditions. Sufficient access and working space shall be provided and maintained around electrical equipment to permit ready access, safe operation, and proper maintenance.
Grounding is an important consideration and must comply with NEC/IEEE standards. The accumulation of static electricity on equipment and personnel is a serious concern in areas that are classified as electrically hazardous. The design engineer has a responsibility to ensure a properly grounded electrical system. This is not a task that should be delegated to the field.
System and equipment lockouts
The NEC (430.102) and OSHA (1910) require a means for disconnecting motors. The lockout should be designed so that each person working on the equipment can put their personal lock on the disconnecting switch.
Equipment and circuitry identification
The identification of equipment should be considered early in the design stage. The NEC (110.22) and OSHA (1910.310) require that all disconnecting means for motors and appliances shall be legibly marked to indicate their purpose. The markings shall be of sufficient durability to withstand the environment involved. This rule, although simple, is often delegated as a low priority to the field installation or operational startup team. The use of duct tape or masking tape with handwritten markers does not meet the intent of the Code.
The human factor should not be overlooked in the design of electrical equipment. The layout, arrangement, and documentation of equipment need the same attention as is given to hardware selection. Physical size of the equipment needs to be considered to reduce lifting and movement risks required to get the equipment to its final location.
Various project/system reviews
Project/system reviews should be held periodically through the duration of the design stages with participation by both the design team (including all applicable disciplines) and client team with operations and maintenance personnel as applicable. These reviews should consist of the following:
- Constructability reviews
- Participation in HAZOPS
- 3-D model reviews
Electrical design safety checklist
Considering the many different types of electrical projects and systems, there is a significant number of design factors that should be evaluated/implemented to ensure life cycle safety. Given the fast-paced schedules of most projects today, there is always the possibility for something to be missed — a reality that has the potential to produce devastating results. In order to minimize this risk, the development and use of an electrical safety considerations checklist, such as the one shown in the Table (click here to see Table), should be used.
The intent of this checklist is to identify topics that should be considered in the design to achieve the safest design possible. It's also recommended that the list be considered a “living” document, which is maintained and updated constantly, including the addition of lessons learned. It's important that all personnel involved with the design are aware of the checklist, have access to it, and use it consistently. Regularly scheduled design reviews for the design team to walk through the checklist will ensure proper considerations are being met.
Codes and regulations exist for the protection of personnel and property. However, it is the design engineer's interpretation and application of these regulations that will lead to a safe industrial processing facility. Field personnel have important inputs with respect to operating procedures, equipment identification, accessibility, and lockouts as well as ergonomic and maintenance issues. Discussions of these topics during the early planning and design stages will provide sufficient opportunity for their inclusion into the final facility.
Ultimately, it is the design engineer's experience and knowledge — in addition to the implementation of developed practices and procedures for life cycle safety — that lead to a facility that is safely designed, installed, operated, and maintained.
Parikh, P.E., is a supervising design engineer for URS Corp., Cleveland, Ohio. He can be reached at [email protected]. Kolodziej, P.E., is a consulting engineer with URS Corp., Princeton, N.J. He can be reached at [email protected]. Salas is an electrical engineer with URS Corp., Denver, Colo. She can be reached at [email protected].
Based on “Electrical Life-Cycle-Safety: The View from the Design,” by Satish Parikh, P.E., Kaz Kolodziej, P.E., and Carmela Salas. © 2009 IEEE.