5.5 Firestop Systems and Ratings

Why Firestopping Matters

A building is divided into fire-resistance-rated assemblies — walls, floors, and shafts designed to contain a fire for a stated number of hours (1-hour, 2-hour, 3-hour). Every time a cable, conduit, or tray penetrates one of those assemblies, the opening is a path for flame, smoke, and heat. Firestopping restores the assembly's rating by sealing the opening with a listed firestop system installed exactly as tested.

For a BICSI Technician, firestopping is not optional and not improvised. Every cable you pull through a rated wall is a penetration you are responsible for sealing with the correct listed system. The exam tests both the rating vocabulary and the installation discipline.

The F, T, L, and W Ratings

Listed firestop systems are tested to ASTM E814 (Standard Test Method for Fire Tests of Through-Penetration Firestops) or the equivalent UL 1479. The test produces up to four ratings:

Not every system carries every rating. A firestop system may be listed with only an F Rating if the assembly does not require a T, L, or W. The system's listing document — the manufacturer's published detail for that exact penetration — states which ratings apply and at what hour-value.

F Rating in Detail

The F Rating is the baseline. It measures how long the firestop blocks flame and the hot gases that would ignite material on the other side. A 2-hour-rated wall requires a firestop with an F Rating of at least 2 hours. The F Rating is the rating most often specified by code.

T Rating in Detail

The T Rating measures heat transfer. Even if no flame passes, a penetration can conduct enough heat to ignite material on the unexposed side. The T Rating caps the temperature rise on the unexposed surface at 325°F above ambient for the rated period. A firestop can have an F Rating higher than its T Rating (flame blocked longer than heat) or vice versa. Where a T Rating is required, the listing must state it.

L Rating in Detail

The L Rating quantifies smoke and gas leakage at a stated pressure differential. Smoke migration is often the real killer in a building fire, and smoke-rated assemblies (typically in healthcare and high-rise construction) require a listed L Rating. The rating is expressed in cfm/sq ft at 0.30 in wc or 75 Pa and may be required at ambient or elevated temperature, or both.

W Rating in Detail

The W Rating measures resistance to water under a hose stream. A firestop that fails under the fire hose is a firestop that fails when firefighters arrive. Not every assembly requires a W Rating, but shafts and wet-area penetrations commonly do.

Fire-Resistance-Rated Assemblies

A fire-resistance-rated assembly is a wall, floor, ceiling, or shaft rated by test (typically ASTM E119 / UL 263) for a stated hour-value. Examples include:

• 2-hour fire barrier wall separating occupancies or smoke compartments.
• 1-hour floor/ceiling assembly between floors of an office building.
• 2-hour vertical shaft enclosing elevator, mechanical, or telecom risers.

The assembly's hour-value is the rating the firestop system must not reduce. A 2-hour wall with a 1-hour firestop is a 1-hour wall after the cable is pulled through it. The firestop system must be rated at least equal to the assembly, and the listed detail must be installed in the exact configuration tested.

Penetration Types

The rating system distinguishes three penetration scenarios, and the listed detail differs for each:

1. Through-penetration. An item passes completely through the assembly — e.g., a cable bundle going through a floor from one room to the room below. Both sides of the opening are sealed.
2. Membrane penetration. An item penetrates one face of an assembly but does not pass through — e.g., a cable entering a wall outlet box, or a conduit stubbing into a box inside the wall. The box itself is the penetration; only one side is exposed.
3. Unpenetrated opening (blank opening). An opening left for future cables must be firestopped with a listed system designed for unpenetrated openings, often a rated blank sleeve or a putty pillow installed now and re-installed after the cable is added later.

Mixing these up on a plan or in the field results in the wrong listed detail being used, which voids the listing.

Listed Systems vs. Field Improvisation

A firestop is not a firestop because someone sealed the hole with putty. A firestop is a firestop because the exact configuration (wall type, opening size, cable type, cable count, annular space, product) was tested and listed by an approved laboratory, and the field installation matches that listed configuration. The listing document is the manufacturer's published drawing that the AHJ and the inspector will compare to the installation.

This means:

• You cannot add cables to an existing firestop unless the listing for that system covers the additional cables and the new cable count.
• You cannot substitute a different product for the listed one, even if it 'looks the same.'
• You cannot resize the opening outside the range tested.
• You cannot omit a component the listing requires (a collar, a backing material, a wrap strip).

Common Exam Confusions

• F vs. T. F blocks flame; T blocks heat transfer. They are independent, and a system can carry one without the other.
• L Rating is not the F Rating. L is about smoke and gas leakage, measured in cfm.
• The assembly's rating is not the firestop's rating. The firestop must be rated to preserve the assembly's rating, not to exceed it by accident.
• A listed product is not a listed system. A can of putty is a listed product; the listed system is the complete tested configuration using that product in a defined opening.

Exam Stance

Expect a question that names an assembly rating (e.g., a 2-hour shaft) and a penetration type (a cable bundle through the shaft wall) and asks which firestop rating applies and what the firestop's rating must be. The answer: a listed system tested to ASTM E814 / UL 1479, with an F Rating at least equal to the assembly's 2 hours, plus whatever T, L, or W the project spec requires, installed in the exact listed configuration.