Intumescent paint is an integral part of effective passive fire protection system. When exposed to extreme temperatures, it rapidly expands to protect the surface that it’s applied to. This prevents, minimises, or delays fire damage to building structures, ultimately providing time for occupants to evacuate safely.
In this guide, Alex Chenery-Howes from CLM Fireproofing explains in greater detail how intumescent paints work, which materials they protect, and how to apply them.
Intumescent paints are able to protect surfaces because of endothermic reactions. They absorb thermal energy from the surrounding environment and undergo a chemical process whereby they rapidly expand (the latin word ‘tumesco’, from which intumescent derives, actually means ‘to swell’). As a general rule, a thin-film coating of intumescent paint will expand at a rate of 50:1, whilst a thick-film coating will expand at a rate of 5:1. This expansion creates a microporous carbonaceous foam which effectively slows down the rate of heat transfer from the fire to the underlying surface.
At the same time, intumescent paints also have an active cooling effect on substrates during fires. They contain hydrates which decompose when exposed to high temperatures, releasing water vapour which cools underlying surfaces.
Intumescent paints are rated according to how long they can effectively withstand temperatures in excess of 250°C – this is the approximate temperature at which the endothermic reaction takes place.
Paints are usually categorised either as 30, 60, 90, or 120 minutes – these times represent the maximum periods that the paint can provide effective passive fireproofing against extreme temperatures. Which paint you select depends on the precise purpose it’s supposed to serve.
Intumescent paint can be used to protect a variety of materials, including steel, timber, concrete, and composites. Here are some of the ways in which it’s utilised with these materials.
The critical temperature of steel is between 350°C –750°C. This is the temperature at which its nominal tensile strength and load-bearing capacity significantly reduces, increasing the risk of structural collapse. Intumescent paint can be applied to a range of steel elements in order to prolong the time it takes to reach the critical temperature. Such elements include beams, columns, brackets, and studs.
The most efficient way to apply intumescent paint to steel structures is by spraying. It can be applied as a base layer directly on the surface of steel, or on top of a compatible anti-corrosion primer. It’s also possible to add a top layer of paint for aesthetic reasons, but it must be approved for use in combination with the intumescent coating.
Timber structural elements, such as beams, char at a rate of 0.8mm/min and release combustible gases, which further fuels fire. Despite certain natural fire-resistant qualities, timber can be fireproofed by an application of thin-film intumescent coating.
Intumescent paint can be applied directly onto the surface of timber structures, either by brush, roller, or spray. There are several varieties of clear intumescent paint that can be used on wood in order to preserve their appearance.
As a non-combustible, non-toxic material with low thermal conductivity, concrete is very resistant to fire damage. Although its precise fire-resistance is determined by factors such as its density, moisture content, and thickness, it can generally withstand temperatures in excess of 900°C without a significant negative impact on its load-bearing capacity.
Intumescent paint can be applied to concrete surfaces by brush, roller, or spray. It’s common to apply paint to concrete ceilings and walls in order to limit and contain fire damage. When combined with other compartmentation techniques (i.e firestopping sealants), it can significantly improve passive fireproofing for concrete structures.
Whether used in residential or commercial buildings, intumescent paint improves the passive fireproofing of a structure. By slowing down the transfer of heat from fires to internal structures (of various materials), it helps to maintain the integrity of a building and ensure that occupants have more time to evacuate.
Further advice on intumescent paint can also be found at the Association of Specialist Fire Protection (ASFP) website. The organisation regularly produces and updates guidance notes for engineers and fire safety professionals on passive fire protection techniques, including the use of intumescent paint in specific instances. Its latest guidance note relates to the protection of structural steel, for instance.
More passive fire protection advice can be found from the following links
Revisit this unmissable webinar to hear from ASFP's Niall Rowan, FPA's Jonathan O'Neill, FSF's Dennis Davies and FIA's Ian Moore on how COVID-19 has affected the fire safety sector. It's essential listening for the current moment.
If there are 2 steel beams next to each other, would they need a 100mm clearance or just 50mm?