Emergency Power Off Systems Explained

Depending on the characteristics of the facility, other standards include requirements for automatic shutdown of power, mechanical systems, or both. Following is an overview of all applicable codes and standards that might require automatic or manual shutdown as published by the National Fire Protection Association (NFPA) and the International Code Council (ICC). This is not intended to be a comprehensive list of all standards referencing shutdown; however, they are the most likely to be adopted by local authorities having jurisdiction (AHJs), and therefore, come with a legal code requirement.

NFPA 70 – National Electrical Code

The primary necessity for a traditional EPO originates from Art. 645 of the NEC, which provides design requirements for electrical systems serving IT equipment, primarily within an IT equipment room. Article 645 is organized as a supplement for special occupancies to the general NEC requirements that would otherwise have to be followed in all other installations. If a space is designated as an IT room per Art. 645, much more relaxed wiring methods are permitted to be used within an environmental air plenum.

From an electrical power wiring perspective, Sec. 300.22 does not allow the use of liquid tight flexible metal conduit (LFMC) or any other non-metallic coated wiring methods within an of environmental air plenum. Likewise, Secs. 320.30, 330.30, and 350.30 require significant securing and supporting of installed cables.

Article 645 allows LFMC to be installed within an environmental air plenum, and does not require it to be secured in place if it is serving IT equipment. It also allows for much more relaxed wiring methods for communication wiring, so long as it is adequately fire resistant or routed in an approved raceway. For operators of data centers or similar spaces, these eased requirements provide highly beneficial flexibility for serving IT equipment through a commonly installed underfloor air plenum. However, this flexibility comes at a cost. For IT rooms, Sec. 645.10 also needs to be complied with. This calls for an approved disconnecting means to disconnect power to all electronic equipment and HVAC equipment, as noted specifically in 645.10:

“An approved means shall be provided to disconnect power to all electronic equipment in the information technology room or in designated zones within the room. There shall also be a similar approved means to disconnect the power to all dedicated HVAC systems serving the room or designated zones and shall cause all required fire/smoke dampers to close. The disconnecting means shall comply with either 645.10(A) or (B).”

The cost of the more flexible wiring methods is the requirement that you install an EPO system for your data center or equipment room. This EPO system must not only disconnect power to the critical IT equipment within the space, but also disconnect power to all dedicated HVAC systems. These requirements are provided to mitigate the additional fire risk associated with the eased wiring methods within an environmental air plenum and allow qualified personnel to quickly and easily disconnect power within an IT equipment room in the event of a fire emergency.

Section 645.10(B) also provides an exception for what is termed a “Critical Operations Data Systems.” As noted in 645.10(B):

“Remote disconnecting controls shall not be required for critical operations data systems when all of the following conditions are met:

“(1) An approved procedure has been established and maintained for removing power and air movement within the room or zone.

“(2) Qualified personnel are continuously available to advise emergency responders and to instruct them of disconnecting methods.

“(3) A smoke sensing fire detection system is in place.

“(4) An approved fire suppression system suitable for the application is in place.

“(5) Cables installed under a raised floor, other than branch-circuit wiring, and power cords are installed in compliance with 645.5(E)(2) or (E)(3), or in compliance with Table 645.10(B)(5).”

Under this exception, the traditional emergency power off buttons may be removed so long as the indicated criteria are met. Most notably, the facility manager must have an approved plan of disconnecting the power to data center equipment, the facility must have qualified personnel available 24/7, and there must be an adequate fire alarm and protection system installed. All of these items should be approved by the AHJ, to utilize this exception, including the classification of the connected loads as a Critical Operations Data System. A Critical Operations Data System is defined in Sec. 645.2 as follows:

“An information technology equipment system that requires continuous operation for reasons of public safety, emergency management, national security or business continuity.”

While this definition can be interpreted broadly, it should be noted that it is like the definition of a Critical Operations Power System (COPS) in Art. 708 of the NEC. Where COPS focuses on power systems, the Critical Operations Data System focuses on IT equipment. Despite the similarities in definition, there is no stated requirement that a facility defined as a Critical Operations Data System must be defined as a COPS and must meet the requirements of Art. 708. The project designer and owner should evaluate the critical nature of facility operations to determine if it lies within the definition of a Critical Operation Data System, specifically with an emphasis on requirements for public safety and emergency management. Should it be determined that the installation does meet the definition, it should also be evaluated if the facility shall be defined as COPS under Art. 645.

NFPA 75 – Standard for the Fire Protection of Information Technology Equipment

NFPA 75 is a building standard or code (if adopted by local AHJ) relating to the protection of IT and associated areas from fire and other associated risks. Unlike the NEC, NFPA 75 is not always adopted in statutory building codes by local jurisdictions. Regardless, the standard represents industry best practice and is frequently followed and referenced in the design of critical facilities. NFPA 75 has two main requirements regarding automatic shutdown — both concerning the release of a clean agent suppression system. The first requirement indicates the need to shut down all electronic equipment in the event of a gaseous suppression system activation. As noted in NFPA 75-2013 8.4.2.1:

“The power to all electronic equipment shall be disconnected upon activation of a gaseous agent total flooding system unless the risk considerations outlined in Chapter 4 indicate the need for continuous power.”

The key term with this requirement is the exception regarding what could be utilized should the risk considerations in Chapter 4 of NFPA 75 warrant a need for continuous power. Specifically, Chapter 4 provides guidelines for the owner, designer or facility manager to weigh the telecommunications risks of an interruption to continuous operation of the IT equipment versus the risk that the equipment could itself be destroyed in the event of a fire. A shutdown of the IT equipment upon release of a gaseous agent could potentially limit the propagation of a fire and assist in its suppression. Life safety concerns should also be a major consideration in this analysis. Specifically, the impact of a fire to the facility occupants should be evaluated versus the impact a loss of power from a shutdown would have on public safety. Examples of where this is a significant concern are facilities serving emergency services or hospitals. Should the exception to remove shutdown be utilized by the owner or design team, the analysis produced per Chapter 4 is recommended to be documented, and if NFPA 75 is legally adopted, approved by the AHJ.

The second shutdown requirement under NFPA 75 is regarding mechanical systems that may exhaust a clean agent from the room upon release, negating its performance. As noted in NFPA 75-2013 8.4.5:

“Where operation of the air-handling system would exhaust the agent supply, it shall be interlocked to shut down when the extinguishing system is actuated.”

This indicates that if a mechanical system would exhaust a clean agent from a protected space upon release, then that system must be shut down upon the actuation of the release. For many data centers and other critical facilities, this requirement is not applicable to primary cooling air handling units, which constantly circulate air within the space, but do not exhaust. Supplemental air handlers that may provide exhaust and outside air to the space are required to be shut down. Primary cooling units would be required to shut down if the installed clean agent system is not designed with adequate agent quantities to protect above ceiling or below floor air handling plenums. In this event, a computer room cooling unit would displace the agent into areas which were not designed to be protected, such as the underfloor supply plenum. This, in turn, would reduce the agent concentration in the protection space where the event occurs.

NFPA 90A – Standard for the Installation of Air-Conditioning and Ventilation Systems

While not typically adopted by many jurisdictions as a statutory code, this standard is indirectly referenced as being applicable per NFPA 101-2015 9.2.1. NFPA 101, Life Safety Code, and is often adopted as a statutory Code in many jurisdictions. NFPA 90A has the following requirement regarding smoke detectors in air streams, which is noticeably different than indicated in the International Mechanical Code to follow.

As noted in NFPA 90A-2015 6.4.2.1:

“Smoke detectors listed for use in air distribution systems shall be located as follows: (1) Downstream of the air filters and ahead of any branch connections in air supply systems having a capacity greater than (2,000 cfm).”

This section also requires smoke detectors to be provided in the air supply system, downstream of any filters and before branch distribution into the space. In a typical data center space, this would equate to providing smoke detectors in the underfloor supply air plenum served by one or more computer room air handling units. Furthermore, NFPA 90A provides a requirement regarding the control of interconnecting control of the smoke detector.

As noted in NFPA 90A-2015 6.4.3.1:

“Smoke detectors provided as required by 6.4.2 shall automatically stop their respective fan(s) on detecting the presence of smoke.”

Upon detection of smoke by the required underfloor smoke detector, the detector shall shut down the associated fans or blowers. Generally, smoke detectors are provided integral to computer room cooling units, either in the return or supply plenums, depending on project requirements. In many cases, these integral smoke detectors shall be wired and programmed to shut down their respective units in the event of smoke detection. An additional option is to utilize system smoke detectors within the supply air plenum to provide the automatic shutdown. However, this could be problematic as such detectors are often used to initiate other fire protection systems, such as clean agent suppression or pre-action sprinklers.

NFPA 101 and NFPA 90A are not always adopted by local jurisdictions, and therefore these requirements may not be a statutory requirement for every project. However, these requirements should still be considered by the project designers, local fire authorities and owner in respect to the fire protection systems installed in the facility and the risk of potentially not providing it. Ultimately, the propagation of smoke or combustion materials is a major risk to both life and property. As is the case with other shutdown requirements, the risk of not shutting down units needs to be evaluated versus the potential risks from the loss of operations.

IMC – International Mechanical Code

The International Mechanical Code (IMC) is a primary mechanical code that is often adopted as a statutory requirement in many local jurisdictions. This code provides requirements regarding monitoring, control and shutdown of mechanical equipment, including the following, per IMC 2015 606.2.1:

“Smoke detectors shall be installed in return air systems with a design capacity greater than 2,000 cfm, in the return air duct or plenum upstream of any filters, exhaust air connections, outdoor air connections, or decontamination equipment and appliances.”

This section indicates that a smoke detector is required to be provided in the return air pathway for all mechanical air handling units over 2,000 CFM. This is contrary to the requirement of NFPA 90A, which requires smoke detectors in the supply air pathway for similar flow values. In a data center environment, this generally includes any floor-mounted computer room air handling (CRAH) units. The code gives further direction regarding control of the mechanical equipment upon an affirmative detection of smoke from its associated smoke detector per IMC 2015 606.4:

“Upon activation, the smoke detectors shall shut down all operational capabilities of the air distribution system in accordance with the listing and labeling of appliances used in the system.”

Per this requirement, smoke detectors in the return air plenum of individual computer room air handling units would be required to shut the unit down in the event of detection of smoke. IMC-2015 606.2.2 goes further to indicate that all air handlers connected to a common supply or return plenum would also be required to be shut down. In a common data center environment of supply and return plenums, this equates to a complete shutdown of the data center cooling systems and likely the IT equipment alongside it. While this may sound worrisome from an operation standpoint, there is an exception to these requirements:

“Smoke detectors shall not be required where air distribution systems are incapable of spreading smoke beyond the enclosing walls, floors and ceilings of the room or space in which the smoke is generated.”

Unlike the requirements of NFPA 90A, if the air handling unit purely circulates air within a single space, smoke detectors and the associated shutdown controls are not required. For most data centers, this will be the case with common computer room air handling units, which circulate air between the space through a series of plenums within the enclosed walls of the space. However, a facility that uses less traditional cooling methods, such as rooftop units outside of the space served, is still required to provide the smoke detectors and associated shutdown controls.

As stated before, the requirements of the IMC differ from NFPA 90A regarding shutdown of mechanical air handling units. Where NFPA 90A requires the smoke detector in the supply of the unit, the IMC requires it in the return. While there are varying benefits to each approach, the correct one is dependent upon adopted codes in a jurisdiction, the project facility layout, and the architecture of the fire detection and suppression systems protecting the space.

Wrap-up

The requirements for emergency shutdown of utilities are a key part of the design and planning of any critical facility. The evaluation of such controls must consider the statutory requirements regarding shutdown as well as a risk evaluation. This analysis must consider the risks and impact of a critical service disruption versus the risks to life and property should emergency shutdown not occur. Each facility will have different requirements based upon the designed system installation and operational mission. It is up to the facility designer to determine the most resilient and safest outcome while maintaining compliance with applicable statutory requirements.       

Danowski is an electrical engineer in the global architecture and design firm’s MEP division at CallisonRTKL, Baltimore, Md., specializing in power infrastructure for mission-critical markets. His experience encompasses the design of electrical systems, including power, lighting, and special systems for data centers, higher education, healthcare, laboratories and government projects. He can be reached at [email protected].