UL 1479 — Fire Tests of Through-Penetration Firestops

The fire-test method behind every through-penetration firestop system listing. Harmonized with ASTM E814.

Last updated: April 22, 2026

Overview

UL 1479 is the fire test standard used to evaluate through-penetration firestop systems — the assemblies that seal around pipes, cables, conduits, and ducts where they pass through fire-rated walls or floors. A firestop system that "meets UL 1479" has been tested as a complete assembly (sealant, backer, pipe, wall type, annular space) and issued a specific UL system number that installers have to follow.

UL 1479 is harmonized with ASTM E814. Both standards describe the same test procedure, use the same ratings, and produce results that apply interchangeably. A system listed under UL 1479 is listed under ASTM E814 by extension, and vice versa.

Scope

UL 1479 applies to firestop systems installed in fire-rated wall and floor assemblies. It covers:

Penetrations by metallic pipes (steel, copper, iron).
Penetrations by non-metallic pipes (PVC, CPVC, polyethylene, ABS).
Electrical cables and cable bundles, both data and power.
Conduits (metal and non-metal).
HVAC ductwork.
Combinations of the above through a single opening.

It does not cover fire-resistive joint systems (gap between two assemblies). Those are tested under UL 2079 / ASTM E1966 — a separate standard.

The Test Method

A representative wall or floor assembly with the firestop system installed is placed in a furnace. The furnace follows the standard ASTM E119 time-temperature curve, reaching approximately 1,700°F at one hour and over 2,000°F at four hours. The assembly is exposed to this curve for the duration of the target rating.

During the fire exposure, the system is evaluated for flame passage and temperature rise. After the fire exposure (or at specific intervals depending on the test), the assembly is subjected to a hose-stream test — a pressurized water spray that simulates the impact of fire-fighting operations. The system has to survive both the fire and the hose stream to pass.

F, T, L, and W Ratings

Every UL 1479 system listing specifies ratings across multiple dimensions. Matching the right rating to the application is what determines whether a listed system is appropriate for a given penetration.

Rating	What it measures	When it matters
F rating	Time the system prevents flame passage and burn-through.	Always. Every penetration needs an F rating at least equal to the wall's hourly rating.
T rating	Time the unexposed side stays below a 325°F temperature rise.	When combustibles could be ignited on the unexposed side — notably, walls separating occupied spaces from electrical or cable runs.
L rating	Air leakage through the system under ambient and elevated temperatures.	Smoke partition performance. Important in hospitals, data centers, and any space where smoke control matters as much as flame spread.
W rating	Water resistance — ability to resist water passage under head pressure.	Horizontal (floor) assemblies, exterior walls, and applications where water ingress from above could cause damage or failure of the firestop.

T-rating gotcha

Many jurisdictions and specifications require a T rating equal to the F rating on walls separating dwelling units, patient rooms, or any space where combustibles on the unexposed side could ignite. Products that pass F but not T are disqualified from those applications. Always verify both ratings before picking a system.

How System Listings Work

A UL firestop system is identified by a system number (e.g., W-L-3001) and describes the exact assembly tested. The listing specifies:

Wall or floor assembly type (gypsum board, CMU, concrete, wood-frame with gypsum).
Wall or floor thickness and rating.
Type, size, and material of the penetrating item.
Annular space allowed (minimum and maximum).
Firestop product(s) required and their thickness or depth.
Any additional materials — backer rods, mineral wool packing, forming boards.
F, T, L, and W ratings achieved.

Installers have to match the real-world installation to the listing exactly. Changing the pipe diameter, the annular space, the wall thickness, or the product depth invalidates the listing. The UL Product iQ database is searchable online by manufacturer, system number, penetrating item, and assembly type.

UL 1479 vs ASTM E814

UL 1479 and ASTM E814 are harmonized standards. The test method, apparatus, and ratings are functionally equivalent. Some specifications reference one, some reference the other, and some reference both. Any firestop system listed under one is accepted under the other.

The IBC references both standards as acceptable test methods for through-penetration firestops. Listing databases published by UL include both designations on each system.

Engineering Judgments

No test library can cover every possible real-world installation. When an installation doesn't match any listed system exactly — a pipe size between tested sizes, an annular space outside the tested range, an unusual penetrant combination — a manufacturer can issue an engineering judgment (EJ).

An EJ is a written opinion from a qualified manufacturer stating that the proposed installation will perform equivalently to a tested system. EJs are accepted by most AHJs but have important constraints:

An EJ only covers the specific installation it was written for. It does not create a reusable listing.
An EJ is only valid while the referenced tested systems and products remain listed. If the manufacturer discontinues a product, the EJ expires with it.
Some AHJs refuse EJs or require independent third-party review.
EJs have to be documented, filed with the project record, and kept retrievable for future audits.

In mission-critical facilities, expect a meaningful percentage of penetrations to require EJs because as-built conditions rarely match listed systems perfectly. Plan for the EJ turnaround time in any remediation project schedule.

Editions & Revisions

UL 1479 is maintained by UL and updated periodically. The IBC references a specific edition through adopted code; local AHJs typically align with the latest IBC edition they've adopted. Most firestop manufacturers list their systems to the most recent UL 1479 edition as a matter of course.

When reviewing system listings for compliance, confirm that the edition cited in the listing meets or exceeds the edition required by the local AHJ.

UL 1479 Listed Firestop Products

Through-penetration firestop products tested to UL 1479 / ASTM E814. Each product carries specific UL system listings — check the product documentation for the system numbers applicable to your assembly.