Fire Separation Walls For Buildings -Firewalls

A fire separation wall is a firewall that is a separate assembly that subdivides a building or separates the adjoining buildings. The wall possesses appropriate resistance to the spread of fire that divides a story or building into a fire compartment. A firewall is commonly constructed of non-combustible materials. 

Fig.1. Concrete Masonry Firewall

A firewall can be used as an ultimate defense against the spread of fire. The firewall withstands the impact of fire and prevents it from spreading by containing it to one side of the wall until the fire burns itself out or is extinguished.

Read More On: Fire Resistance of Concrete 

Fig.2 Precast Concrete Firewall Temporarily Braced During Construction

The firewall design must not result in the collapse of the firewall which could result in total building collapse (Section 706.2 of the 2012 IBC). When a single firewall cannot guarantee the complete protection of the building against fire, the firewall needs to be constructed by two separate walls. This is called as a double firewall. 

In the case of a double firewall, each wall possesses a fire-resistance rating of at least half of that required for the firewall. Double firewalls provide high fire resistance even in severe fires, that remains standing and avoid building collapse. Here, the side of the wall facing fire must only be fire-collapsed and the remaining wall on the side opposite to the fire must remain standing. (2012 IBC w.r.t NFPA 221).

The normal thickness of firewalls are 2 inches that are installed at least 3/4th of an inch away from the wood-studs or the steel-stud framing. 

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Need for Firewalls

Firewalls are necessary to:

  • Contain fires and limit property damage
  • Protect the building occupants
Fire walls are a type of fire resistance rated construction. Fire resistance rated construction is a passive form of fire protection system that imparts resistance as the fire advances. It is opposite to active fire protection systems like automatic sprinkler system that tries to suppress a fire.

Fire Rating of Firewall

The fire rating of firewall used for fire separation in structures is expressed as:

  1. Fire Protection Rating
  2. Fire Resistant Rating

1. Fire Protection Rating

Fire protection rating is a parameter that indicates the duration of the fire test exposure to which an opening protective assembly was exposed (like firewall). 

2. Fire Resistant Rating

This is defined as the time in minutes or hours that the materials or assemblies have withstood a fire exposure as determined by tests or methods as per the test conducted by the standards. It is a indication through the duration of the fire test exposure of an opening protecting assembly like firewall.

The below chart shows the firewall groups with different fire-resistance rating in hours as per IBC 2012.

For example, the fire ratings range from 2 hours for Storage facilities (Group S) and Factories (Group F) to 4 hours for High Hazard facilities (Group H). In addition, Tables 721 in the 2012 IBC lists minimum fire resistance, in hours, of various structural components.

Design Recommendations for Firewall

The materials used to design a firewall must follow ASTM E 119 (Standard Method of Fire Testing of Building Construction and Materials). 

ASTM E 119 specifies fire‐endurance tests, which include placing a sample of a firewall in a furnace and heating it to a certain temperature for a specified length of time. Data collected during the test includes the length of time for which the wall remains structurally intact and the ability of the wall to limit the amount of heat passing through it. Similar testing requirements are also provided by Underwriters Laboratory, UL Standard 263.

                        Also Read: Step by Step Inspection of Building Structures