Article 708: Critical Operations Power Systems

Nov 1, 2007 12:00 PM, By Michael A. Anthony, P.E., University of Michigan; Robert G. Arno, EYP Mission Critical Facilities

Find out how this new article, which is part of an effort by NFPA to meet the government’s need for improved power security standards, affects you

Focusing on the complex interplay among mechanical and electrical systems needed to support critical infrastructure, Art. 708 is one of four new Articles added to the 2008 NEC. Reaching deep into the conception, commissioning, and management of such systems, it references eight other standards, annexes, and additional explanatory material in the NFPA portfolio of documents that are bound together — either in whole or in part — by their interlocking emphasis on power security.

In an initial attempt to develop the content for this new Article, Technical Panel 20 debated whether the instruction from the NFPA Standards Council to do more about power security at the building premises level was a directive about an occupancy or a system. As a special occupancy, it belonged in Chapter 5. As a system, however, it belonged in Chapter 7.

In an environment that requires a game-changer to get public safety departments and facility managers thinking fast about the survivability of critical power systems, the point is moot. Survivability requires a facility (a designated critical operations area or DCOA) and a system (critical operations power system or COPS). The desired result does not happen overnight, and electrical professionals cannot simply specify reliability from a table — as we would refer to Table 250-66 when sizing a grounding electrode conductor (see Reliability vs. Availability).

Reliability assessments based on probabilistic methods provide more consistent results, reflecting both the condition of existing equipment and the basis for design. Manufacturing philosophies such as “total-quality management” (TQM) and “six sigma” were widely deployed years ago — often with good results. Technical Panel 20 contemplated a similar deployment in Art. 708. In fact, as a method for improving availability using parametric models to derive design values of reliability from operational values, TQM is cited in new Annex F.

Addressing risk assessment

Adopting jurisdictions will now have to prepare and document a risk assessment. As per 708.4(A), “In critical operations power systems, risk assessment shall be performed to identify hazards, the likelihood of their occurrence, and the vulnerability of the electrical system to those hazards.”

As with other NFPA documents, such as NFPA 110, “Standard for Emergency and Standby Power Systems,” which requires a written log of generator testing, technical committees assume that mandatory documentation forces facility managers to do certain things that would not otherwise be done if a written record were not required. Local public safety organizations may find that just putting people around a table to do a risk assessment adds value to existing, everyday routines — not just during times of operational discontinuity.

Sample risk assessment from the emergency management division of Washtenaw County, Mich. Note that earthquakes in southeastern Michigan are ranked relatively low and that infrastructure hazards are relatively high.

One simple method of producing a risk assessment is as follows:

A) Identify control boundaries of the system. Is the facility stand-alone or part of a multi-function building? For example, is it shelter in place, off-site, or system + system?

B) Identify every conceivable disaster for the facility and location. Examples appear in Sec. A.5.3.2 of NFPA 1600, “Standard on Disaster/Emergency Management and Business Continuity Programs.”

C) For each disaster, determine a relative probability (1 = less likely; 5 = more likely). This stage may entail research specific to location, industry, and other organizational characteristics.

D) Assess the business impact of each disaster (1 = moderate; 5 = severe). Consider the effect upon public safety officers, hazardous material handlers, dispatch personnel, etc. — anyone who would be involved in disaster recovery functions.

E) Assess your ability to respond to each disaster in light of resource availability. Does your organization have the requisite resources either in-house or through third parties? (1 = sufficient resources; 5 = absence of resources).

F) Calculate a rigorous risk assessment for each disaster by multiplying columns C, D, and E. Normalize the figures, and rank accordingly.

An example of one county's risk assessment appears in the Table above.

Another more sophisticated method for preparing a documented risk analysis appears in Sec. A.5.3 of the Explanatory Material in Annex A of NFPA 1600, where failure mode and fault-tree analysis are described. The validity of more sophisticated studies will be dependent upon the competence of the expert agency, on the credentials of the team, and on the depth of the team's analysis.

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