Fire Ratings: Do You Need One?

By Ron Kight | March 16, 2021 | A/E Indusry News, Architects/Owners, Electrical

Introduction

This blog will attempt to answer the age-old question “Does this electrical room need to be fire rated?”.  Well, we are here to clear the air with an emphatic….maybe. 

Electrical rooms in and of themselves do not require fire ratings because they are labeled “electrical room” but may need to have rated partitions depending on the type of equipment contained therein or the ratings of the adjacent spaces.  For example, if an electrical room is sharing a wall with an egress corridor or stairwell, the rating of the enclosure must be maintained, even if the electrical room is not required to be rated. This blog is not intended to cover all situations, nor local specific requirements. We will attempt to tackle the most common scenarios for fire rating requirements as dictated by Nationally accepted Code requirements. 

Transformers

The most common piece of electrical equipment that may require a room to be fire rated is a transformer.  NFPA 70 (National Electrical Code or NEC) Article 450.21 states that for transformers (35,000 Volts or less) sized 112.5kVA or larger shall be installed in a transformer room of fire-resistant construction of a minimum fire rating of one hour. However, there are two very significant exceptions to this fire rating requirement, both involving the transformer insulation.  Your engineer should be familiar with both exceptions and advise if fire rating considerations are necessary.  In Proficient’s experience, most commercially available transformers of this voltage range and kVA rating will meet the insulation requirements to avoid fire rating the space.  If the transformers are over 35,000V or the transformer is oil-filled, the transformers shall be installed in a vault constructed in accordance with Part 3 of NEC article 450.  The fire rating requirements for a vault is a minimum of three hours. Vaults most typically occur where the utility transformer will be located within the building or for larger campus style projects, where the Property Owner also installs and maintains the building-to-building electrical distribution.  Bear in mind that transformers will also need ventilation, so initial consideration must be made for adequately protecting any openings.  

    Transformer Room

    Generators

    The second most common piece of electrical equipment that will trigger a fire rating is generators.  If your project has a generator that serves emergency power systems such as emergency lighting, the generator shall be installed in a room of two-hour rated construction as per NFPA 110 (Standard for Emergency and Standby Power Systems) Article 7.2.1.1.  This two-hour rating would also apply to ventilation air for combustion and exhaust ductwork.  This ductwork requirement is oftentimes limited by placing the generator in a room with two exterior wall exposures, and therefore restricting the amount of ductwork routed inside the building. The fire ratings associated with generators could be avoided by locating the generator in an exterior location in a weatherproof enclosure either on the site or roof of the building.   

      Heavy Duty Back Up Diesel Power Generator 

      Building Occupancy

      Building occupancy can also have an impact on fire rating requirements. For equipment, uninterruptable power supplies (UPS), cables, or raceways serving emergency systems or generator control wiring in assembly occupancies for no less than 1,000 persons, high-rise buildings, or educational occupancies with more than 300 occupants, the raceways shall be protected by a two-hour listed electrical circuit protective system or two-hour fire rated assembly, unless fully protected by an approved automatic fire protection system.  

      Another occupancy situation that typically requires a fire rating is when generators are associated with Health Care Facilities.  If your project has a generator that serves health care areas, the generator shall be installed in a room of two-hour rated construction as per NFPA 99 (Health Care Facilities Code) Article 6.7.1.2.3.  This two-hour rating would also apply to ventilation air for combustion and exhaust ductwork. As previously mentioned, these fire ratings could be avoided by placing the generator in an exterior location in a weatherproof enclosure either on the site or roof of the building. This code is oftentimes referenced by additional codes and not necessarily enforced solely as an entire document.  Have you engineer verify the applicability of NFPA 99 to make sure the requirements apply to your specific project.  If applicable, certain sections of the provisions of NEC Article 700 are also enforceable.   

        Fire Pump Conductors

        In addition to transformers, generators, and occupancy, fire pump conductors can play a role in fire rating requirements. As per NEC articles 230.6, 230.9, and 695.6, fire pump conductors shall be routed outside of the building.  Where conductors cannot be located outside of the building, they shall be protected from a fire for two hours. There are multiple methods in which this can be achieved, so anytime a fire pump has been identified to be required for a project, coordinate with your engineers early and often to make sure these requirements can be met with the least impact to the overall design.  

          Industrial Plant Fire Pump Controller System 

          Closing

          All in all, does your electrical room need to be fire rated? The answer to this question varies on a number of factors. Most commonly, equipment such as transformers and generators as well as occupancy and fire pumps can trigger a necessary fire rating. However, by consulting your engineer early, you can find out the proper exceptions and provisions to avoid such situations and mitigate the impact on your overall building design.