Fire resistant paint is a substance that can delay and prevent the spread of fire for a specific period of time. It is important to remember that no substance is completely incombustible. The paint does not extinguish or stop fire; it only contains it and protects the structures to which it is applied.
Fire resistant or fire retardant paint is intumescent, meaning it swells when exposed to high temperatures and increases in volume while decreasing in density. When fire resistant paint swells, it forms an insulating char that conducts heat poorly and allows more time for the fire to be contained by firefighters.
Intumescent paint is a form of passive fire protection, which describes products that raise fire resistance and reduce the spread of a fire. These products also help maintain the structural integrity of a building and preserve lives by giving residents more time to escape before the fire becomes uncontrollable. Fire resistant paint carries a fire resistance rating that describes how long the product can withstand fire.
When fire resistant paint comes into contact with heat, the paint increases in volume 200 to 300 times. This can happen at temperatures as low as 300 degrees Fahrenheit (148.8 degrees Celsius). Combustion takes place at 850 degrees Fahrenheit (450 degrees Celsius). The insulating layer protects surfaces underneath from the heat and delays the amount of time it takes for the structure to heat to a combustible temperature. As fire continues, this foaming and insulating process may be repeated multiple times until the fire is extinguished or the paint has been burned through.
Most paint is used for decorative purposes, but intumescent paint has the additional purpose of protecting underlying structures from fire damage. Some fire resistant paint is available in a variety of colors. Others are designed to be used like a primer and applied underneath regular latex paint. Fire resistant paint may be sprayed, rolled, or brushed on, just like decorative paint. It can be applied to a variety of porous surfaces.
Fire retardant and resistant paints first became available in the early 1950s. They were expensive to use, difficult to apply, created undesirable fumes, and contained formaldehyde, a known carcinogen. By the 1980s, the first intumescent reactants were produced. These were different from its predecessors in that the paint bonded to a variety of surfaces and contained no carcinogens, meaning it was safe to be used around people and animals.