Is Transformer Firewall Protection Really Required?

Is Transformer Firewall Protection Really Required?
Detailed Design Engineering Engineering Design

Is Transformer Firewall Protection Really Required?

Is Transformer Firewall Protection Really Required?

Transformers are oftentimes filled with oil for insulation, to prevent electrical arcing, and to serve as a coolant. This oil is similar to mineral oil and very flammable. When a transformer fails it can lead to intense fire and a violent explosion. Transformers can hold anywhere between a few gallons to thousands of gallons. Transformers can be installed indoors or outdoors, but indoor transformers typically are not filled with oil while outdoor transformers often are.

IS: 10028 ( Part II) Code of practice for selection, installation, and maintenance of transformers section 3.6.2

If two or more transformers are installed side by side, they shall be separated by fire-separation walls. Fire separation walls are deemed to be adequate from the fire-safety point of view, even if the oil capacity of individual transformers does not exceed 2000 liters, and the total capacity of all transformers installed side by side exceeds 2000 liters.

NFPA 850, Recommended Practice for Fire Protection for Fire Protection For Electric Generating Plants & High Voltage Direct Current Converter Stations, Section 6.4.1

Outdoor oil-insulated transformers should be separated from adjacent structures and from each other by firewalls, spatial separation, or other approved means for the purpose of limiting the damage and potential spread of fire from a transformer failure. Type and quantity of oil in the transformer

Once this analysis has been completed, any decisions made as a result should be included as part of the Fire Protection Design Basis Document.

Outdoor Oil-Insulated Transformer Separation Criteria

Transformer Oil Capacity

Minimum (Line-of-Sight) Separation Without Firewall













>5000 >18,925 50


It is recommended that adjacent oil-insulated transformers containing 500 gal (1893 L) or more of oil be separated from each other by a 2 hour–rated firewall or by spatial separation.

Oil-insulated transformers or other oil-filled electrical equipment of greater than 100 gal (379 L) oil capacity installed indoors should be separated from adjacent areas by fire barriers of a 3-hour fire-resistance rating.

Transformers have a rating greater than 35 kV, are insulated with a less flammable liquid or non-flammable fluid, and installed indoors and should be separated from adjacent areas by fire barriers of a 3-hour fire-resistance rating.

Where transformers or other oil-filled electrical equipment are protected by an automatic fire suppression system, the fire barrier fire resistance rating should be permitted to be reduced to 1 hour.

CEA Technical Standards for Construction of Electrical Plants and Electric Lines) Regulations, 2010. Clause 54

33 kV voltage rating transformers shall be separated from one another by a firewall.

IS 3034 Fire Safety of Industrial Buildings: Electrical Generating and Distributing Stations, Section 4.4

The plant shall be sub-divided into individual fire areas, Such subdivision by fire barriers or separation walls of a minimum 2 hours of fire resistance shall be provided in the following cases:

  1. Between transformer yard/outdoor transformers and other nearby buildings, in case a clear distance of 15 m is not available.
  2. Between individual oil-field transformers containing oil in excess of 2 000 liters in case clear distance as specified in IS 1646,1982 is not maintained

IS 1646, Section 7,  Code of Practice For Fire Safety Of Buildings (General): Electrical Installations

Separating walls are necessary between transformers having an individual or aggregate oil content of 2000 liters.

Separating walls shall not be necessary in the case of transformers having an aggregate oil capacity exceeding 2000 liters but an individual oil capacity of fewer than 5000 liters if the distance between transformers and other apparatus is more than 6 m or if the transformers are protected by an approved high-velocity water spray system.


The type and design of transformer firewalls are dependent on multiple factors. Designers should have a thorough understanding of the relevant codes and standards. Major factors to be considered – Size of a postulated oil spill (surface area and depth), Type of construction of adjacent structures, Type and amount of exposed equipment, including high line structures, motor control center (MCC) equipment, breakers, other transformers, and so forth, The power rating of the transformer, Fire suppression systems provided, Type of electrical protective relaying provided, Availability of replacement transformers (long lead times), The existence of fast depressurization systems.


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