Firestop Overview Part 2

Basic Situation

An uncontrolled fire is a danger for both people and property. In spite of numerous regulations and precautions, the outbreak of fire can never be completely prevented. Common sense and careful handling of volatile materials remain the most important protective measures against the outbreak and spread of fire.

The Mechanics of Fire

Three things must be present to start a fire:

  • There must be a heat source (flames, space heater) — note that some materials, under the right conditions, can generate their own heat and ignite spontaneously
  • There must be a fuel source (wood, paper or combustible materials)
  • There must be oxygen (air)

In a closed room a fire develops in three phases: origin, development and extinguishment

Origin: In this phase, the three factors in the triangle of fire exist in a type of reciprocal relationship (depending on the fuel present). The fire starts and the amount of flammable materials contributing to the fire expands, generating smoke along with an increase in temperature.

Development: Spontaneous combustion of flammable materials in a closed room occurs in this phase and is characterized by a socalled “flash-over”. The time frame for a flash-over depends on the location of flammable materials in the room as each base material has its own flash-over point. The rate of flame spread can vary from 3 to 15 minutes leading to increased heat generation and air movement. The temperature can rise as high as ~1800°F.

Extinguishment: As the flammable material is consumed, the temperature drops. Once all flammable material has been burned, the fire loses one of its required ingredients (fuel source) and, therefore, naturally burns out. The fire can also be stopped by removing the oxygen source or by cooling the room through extinguishing measures.

Fire Protection Terminology

Stability — A measure of the structural stability of a building component when exposed indirectly to heat from a fire or directly to flames from a fire.

Integrity (F-Rating) — A measure of the amount of time that it takes for flames to reach from the fire side of an assembly to the non-fire side of an assembly.

Insulation (T-Rating) — A through penetration firestop test standard (ASTM E814) that measures the time (T-rating) it takes for the non-fire side of the assembly to reach 325°F + the ambient temperature.

Depending on the building dimensions, location, and intended usage for the structure, the building must be designed to contain fire within compartmentalized sections of the building for established periods of time. These periods of time are known as the fire rating. The principles of compartmentalization are designed to limit the spread of fire and to provide evacuation paths for building occupants. Building compartmentalization also allows for emergency personnel to effectively extinguish the fire.

Time-Temperature Curve — ASTM E119 is the time-temperature curve test standard referenced for firestop testing. This test standard requires that the air temperature within the testing furnace ramp up to a specific temperature within a given amount of time and then maintain that temperature for a specified time period. This simulates the conditions of a “typical” fire in an uncontrolled environment while having the advantage of studying the fire’s behavior in the controlled environment of a testing furnace.

How Firestop Products Work

Firestop products, when installed according to a tested system, withstand the high thermal and mechanical pressures present during a fire while maintaining their functionality and integrity in different ways.


When exposed to heat, the material chars and forms a carbon-like insulating layer that serves to protect the penetration opening. (Examples: CP 618 Firestop Putty Stick, CP 617 Firestop Putty Pad)

Intumescent with Pressure:

When exposed to heat, the firestop material expands producing pressure. The pressure causes the openings where the firestop is placed to be closed-off from the fire. (Examples: FS-ONE MAX Intumescent Firestop Sealant, CP 643N/644 Firestop Collars, CP 648-E/S Firestop Wrap Strip, CP 653 Speed Sleeve)


Insulating materials are poor conductors of heat making it difficult for heat generated from a fire to transfer and spread across the firestop material. (Examples: CP 620 Fire Foam, Mineral Wool)


The firestop material chars and forms a carbon-like insulating layer that serves to protect the penetration opening. (Examples: CP 606 Flexible Firestop Sealant)

Non-Flammable Material: The firestop material reinstates the integrity of an assembly. (Examples: CP 637 Firestop Mortar) Reduced Expansion of Flames:

The firestop material contributes no fuel or energy to the fire. (Examples: CFS-S SIL GG/SL Firestop Silicone Sealant)

Range of Application

The image to the right shows several typical firestop applications. Hilti firestop products are designed, tested and approved to help protect both life and property from the damaging effects of fire, smoke and noxious gases. To restrict the uncontrolled spread of fire, walls and ceilings of a fire compartment must be able to contain the fire and prevent fire spread for a period of time. The integrity of openings and gaps in fire-rated compartments, such as those shown in the image to the right, must be restored by a tested system, or an engineering judgment if no tested system is available, to restrict heat transfer and the passage of flames, smoke and gases. Firestopping applications range from walls, floors and ceilings and consist of various forms and materials. The following applications must be considered when specifying:

  • Perimeter joints
  • Construction joints
  • Through penetrations

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