Steel RMC, IMC and EMT do not require fire resistance ratings. Fire resistance ratings apply only to assemblies in their entirety. Building codes consider steel conduit and tubing to be non-combustible. Fire testing is not required by the UL standard to which these products are listed, however, steel RMC, IMC and EMT have been exposed at UL to the ASTM E119 time temperature curve for up to four hours in duration. This was done during testing of annular space filler, and the temperature reached almost 2000 F. The conduit / tubing was still intact at the end of the test. This information is contained in a report entitled “Annular Space Protection of Openings Created by Penetrations of Tubular Steel Conduit — A Review of UL Special Services Investigation Investigations File NC546 Project 90NK11650,” which is available for downloading here. Since the conduit / tubing was tested without conductors, the condition of the insulation of the conductors within cannot be verified when subjected to that temperature.
Penetration of fire-resistance rated assemblies
The raceway installer shall determine if the walls, floors or ceilings are fire-rated prior to installing raceway systems. Penetration openings shall be properly filled for fire safety, using approved materials. The NEC® and building codes require that openings around raceways which penetrate a fire-resistance-rated assembly be sealed to prevent the spread of fire and smoke from one area migrating into another.
NOTE: This can be accomplished by use of a listed penetration firestop system, or by use of annular space filler in accordance with building code exceptions.
There are many listed penetration firestop systems which can be used with steel conduit / tubing to seal openings; the listing instructions shall be strictly followed.
NOTE: It is often incorrectly assumed that if steel conduit or EMT penetrates a fire-resistance-rated assembly, these products also must be “fire-resistance-rated.” Steel conduit and EMT are non-combustible and do not require a “fire-resistance-rating.” The codes require that the annular space around the steel conduit be properly filled so that the fire-resistance-rating of the assembly is maintained.
Most building codes permit openings around steel RMC, IMC and EMT that are penetrating concrete or masonry to be filled with cement, mortar or grout. However, since local codes sometimes vary, the local requirements should be checked prior to installation. Also, project specifications often describe exactly how these openings are to be filled, even though the codes might permit other methods. Firestop systems listed for use with steel conduit / EMT are permitted to fill the space surrounding the conduit or tubing.
In all cases, the raceway installer shall use materials which ensure that fire-resistance ratings of the penetrated assembly are not degraded by the installation of a raceway system.
Penetration of non-fire-rated assemblies
In non-fire-rated assemblies, when non-combustible penetrating items such as steel conduit and EMT connect not more than three stories, the space around the penetration must be filled with an approved non-combustible material to resist the passage of flames and products of combustion. This is called fireblocking.
If the penetrant connects not more than two stories, the annular space filler does not have to be noncombustible, but it must be an approved material that resists the passage of flames and the products of combustion.
Thermal protection of steel raceways
The NEC and local or state code requirements for fire protection of emergency systems and fire-pump circuits shall be reviewed prior to installing these circuits. Local codes sometimes vary from the NEC. Steel raceways withstand fire; however, ordinary conductor insulation melts when exposed to elevated temperatures, and a short circuit can be created. This is the reason for special protection of emergency and fire-pump circuits.
Methods of thermal protection include putting the conduit / tubing in a fire-rated enclosure such as a chase (horizontal or vertical), embedding in concrete, using a listed wrap system for protection from fire or using circuit integrity cables within conduit as part of a listed Electrical Circuit Protective System. (See UL Fire Resistance Directories (Category FHIT)).
NOTE: Fire wraps can affect the temperature of the conductors, and the need for ampacity derating must be determined. It is also important to determine that the support system is protected and will withstand the fire exposure.
The NEC does not require these thermal protection methods for emergency systems where conduit is installed in a fully sprinklered building. Local codes shall be consulted, and the requirements of the applicable code and / or project specification must be followed.