Fire retardant

Workers apply intumescent paint to a floor beam at the 44th Street facility. Source: MTA Construction & Development Mega Projects.

1 Introduction
2 History
3 Fire retardant or flame retardant?
4 Related articles on Designing Buildings

[edit] Introduction

A fire retardant is a substance such as a coating, powder, foam, gel or spray, that is used to slow - and eventually stop - the spread of fire. It is a preventive measure that can help limit a fire’s spread by triggering a chemical reaction.

[edit] History

The earliest form of fire retardants (which were thought to have originated many centuries ago) were substances such as vinegar, alum and clay that were used to treat timber and some fabrics.

More complex fire retardants were introduced in the 19th century in the form of flame retardants for fabrics. These were developed by Joseph Louis Gay-Lussac, a French chemist who made a number of discoveries in the idea of temperature and its relationship to gas pressure (Gay-Lussac’s Law or Amontons's law).

His exploration of the use of salts as fire retardants was groundbreaking, but it wasn’t until the 1900s that more effective measures would be introduced in the form of flame retardants.

[edit] Fire retardant or flame retardant?

Modern fire retardants and flame retardants have similar purposes - to control fires - but they achieve this by different methods:

Flame retardants are chemicals (such as aluminium hydroxide) usually applied to combustible materials (such as textiles, plastics and coatings).
Fire retardants are chemicals (for example, ammonium and diammonium sulfate) that can also be used on surfaces, but different types of chemicals are used for different purposes. Fire retardants as extinguishers include chemicals that will absorb a great deal of heat to cool whatever has been treated. Other agents will react with the heat to put out the fire by releasing water vapour or carbon dioxide. This is a physical process called dilution. Other fire retardants are intumescent coatings (such as paints or plastic additives). These rely on substances that will expand through a chemical reaction when heated to protect the materials that have been coated. For more information see: Intumescent coatings.

NB Fire retardants can also be dropped from planes to extinguish forest fires.

Fire safety in construction, written by HSE and Published by TSO (The Stationery Office), Third Edition, 2022, suggests that the terms fire-retardant, flame-retardant, fire-proof and flame-proof: ‘…are used to describe materials that do not burn particularly well. When they are used to describe sheet materials, it normally means that a fire will not be any worse if they are present – although they will typically burn or melt away if they are close to an existing fire. When these terms are used to describe treatments applied to materials, they normally mean that it takes a longer time and/or a larger fire to make them burn, and that when they are on fire the flames spread more slowly. Often, they are tested for effectiveness only in small fires, and may not perform as well if exposed to a larger fire.’