By David Stymiest, PE, CHFM, CHSP, FASHE
Healthcare facility emergency power systems are held to a very high standard. They are expected to deliver power to what they must, when they must, for as long as they must. A review of some medical journals will find references to clinical expectations for “uninterrupted power supply” and similar phrases. In fact uninterrupted power is not guaranteed despite the misconceptions of some clinical personnel. Hospital power systems are not as robust as large data center power systems, and even data center power systems sometimes fail. But healthcare facilities can take steps to reduce the probability of emergency power failures.
Firstly it is helpful to understand the differences between reliability, availability and dependability. Reliability can be considered the probability that a system operates and gives the same result on successive trials. Availability on the other hand can be considered the probability that a system will function at any instant required, including the next instant, and for as long as required from that point. And finally dependability can be considered as the metric that measures availability, reliability & maintenance support.
The Joint Commission’s (TJC’s) Sentinel Event Alert Issue 37 (SEA-37), entitled “Preventing adverse events caused by emergency electrical power system failures” was published in 2006. TJC addressed that topic again in EOC News in 2007. Power system failures during recent natural disasters indicate that we should consider addressing the SEA-37 power system vulnerability analysis again. This time we should also make sure to address potential common-mode failures, which are failures of two or more systems or components due to a single event or cause.
One way to reduce vulnerabilities is to find and then eliminate the potential for common-mode failures. A safety engineering concept considers that once a failure mode is identified, it usually can be mitigated by adding extra or redundant equipment to the system. However you cannot correct what you have not yet identified, and the existence of an uncorrected common mode failure potential removes the advantage of such redundancies.
It is helpful to take another look at existing conditions from a fresh perspective. There are many examples of potential common-mode failures, including single power sources to redundant equipment, common wiring, common feeder or equipment locations, susceptibility to the same internal or external hazards, and lack of maintenance. Many organizations consider external flooding, but what about the rupture of a chilled water line or domestic water line in a mechanical room adjacent to an emergency power equipment room? One major lesson learned from the past few years’ emergency power failures is that we really should sweat the small stuff. Things break, and details are critical. When failures do occur, power failure procedures that have been thoroughly considered before an incident are likely to be more effective than those developed afterwards.
An effective approach to resolving potential vulnerabilities is to:
- Consider each component that must operate successfully
- Use the “what if” analysis technique to determine all scenarios that can cause it to fail
- Determine whether any of these scenarios will also cause redundant components to fail
- Address the resulting potential common-mode failures
Having dependable emergency power systems requires regular maintenance of all components. Maintenance will reduce operational vulnerabilities related to normal wear and tear. All emergency power supply system equipment and systems need to be maintained in full accordance with all applicable requirements as stated in NFPA 110:
8.1.1 The routine maintenance and operational testing program shall be based on all of the following:
- Manufacturer’s recommendations
- Instruction manuals
- Minimum requirements of this chapter [Ch. 8 - Routine Maintenance and Operational Testing]
- The authority having jurisdiction
The requirement for maintenance includes automatic transfer switches, themselves a potential source of common-mode failure. Many hospitals are not presently performing required maintenance on automatic transfer switches because of equipment and operational restrictions, thereby increasing potential vulnerabilities. Although they are not required by codes and standards, isolation-bypass transfer switches represent a best practice that permits required maintenance without taking that branch out of service.
This article is based upon the author’s more comprehensive article entitled “After the Storm – Expanding the concept of emergency power reliability” that was originally published in the January 2013 issue of Health Facilities Management magazine, Vol. 26, No. 1. ©2013 by Health Forum Inc. Contact the author at dstymiest@ssr-inc.com for a digital copy of that HFM article.
NFPA DISCLAIMER: Although the author is Chairman of the NFPA Technical Committee on Emergency Power Supplies, which is responsible for NFPA 110 and 111, the views and opinions expressed in this article are purely those of the author and shall not be considered the official position of NFPA or any of its Technical Committees and shall not be considered to be, nor be relied upon as, a Formal Interpretation. Readers are encouraged to refer to the entire text of all referenced documents. NFPA members can obtain NFPA staff interpretations at www.nfpa.org.
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