Intumescent fireproofing is often a crucial component of a passive fire protection strategy. While application methods can vary, it involves applying a protective coating to structural steel. In the event of a fire, intumescent coatings increase the length of time before the steel begins to lose its structural integrity.
It is estimated that structural steel can withstand temperatures of up to 425°C before it begins to deteriorate. At this point, the intumescent paint expands to form an additional carbonaceous layer (otherwise known as a ‘char’). This is because intumescent paint contains endothermic compounds which expand when exposed to heat, protecting the steel without affecting its mechanical properties.
This article will show how intumescent fireproofing works with an introduction to various methods, as well as practical considerations for using intumescent coatings in a passive fire protection project.
Intumescent fire protection and industry regulations
Those about to initiate an intumescent fire protection project should refamiliarise themselves with industry requirements. For example, British standards specify that the ‘critical failure temperature’ for load-bearing steel beams carrying a concrete slab cannot be lower than 620°C; this temperature decreases to 550°C if the beams are exposed across four sides. It’s important to note that European standards are more specific. In Europe, the critical temperature of steel beams depends on whether they are fully loaded, and if the beam is carrying minimal weight the expected temperature limit is considerably higher than in the UK.
Fire safety: Approved Document B is the main regulatory guideline for structural fire safety in England. It specifies that buildings must be designed and constructed to withstand fire for a ‘reasonable period’. This period is usually classified as either 30, 60 or 90 minutes based on the building’s height and occupancy (for example, if it is an office building or a residential tower block). This is particularly important as it will affect the classification of a particular product used for intumescent fireproofing (e.g. a fire resistance ‘rating’ of 30, 60 or 90 minutes).
For more information about regulatory requirements for the fire protection of structural steel, below are several useful reference points:
- BS EN 1991: Actions on Structures: This offers specifications for designing buildings to ensure optimal levels of fire resistance, with an emphasis on how fire affects a structure’s mechanical properties.
- BS EN 1993: Design of steel structures: This guide defines best practices for ‘safety and serviceability’ when designing steel structures, more specifically their durability in the event of a fire.
- BS EN 1994: Design of composite steel and concrete structures. These guidelines are similar to BS EN 1993, except they refer specifically to buildings made using concrete or composite steel.
Intumescent fire protection methods
Projects can vary significantly in their deadlines and available resources, not to mention the building’s design and structural features. Therefore, when choosing an intumescent fireproofing method, you should weigh up their distinct advantages and limitations to determine whether they will offer your desired results.
Intumescent paints can be either solvent or water-based and applied using a brush, roller or spray. The paint is applied to the steel in a series of thin layers, but once exposed to high temperatures these layers can swell up to 50 times their original thickness. Intumescent paint offers various practical benefits. For example, there are fewer difficulties when applying the paint based on the size or shape of steel beams or columns, and the application process can take place both on-site and off-site. Intumescent paint offers more scope for decorative finishes.
Thin and thick film coatings
Film coatings are the most common method of intumescent fire protection in the UK. They consist of three main layers: a primer, a base coat and a sealer coat. Thin film coatings are the industry standard and expand at approximately the same rate as intumescent paint. Regardless of whether a building’s fire resistance rate is 30, 60 or 90 minutes, it can usually be accommodated with a thin film solution. In comparison, thick film coatings are common in high-risk environments where extreme temperatures are the norm (such as industrial plants). That said, if a project specification includes the need for a decorative finish then a thick film coating is also a viable solution.
It’s also worth noting that intumescent paint is not the only approved method of protecting structural steel from fire damage. If teams are working on a strict turnaround and their progress is being hindered by factors such as hazardous weather conditions or accessibility issues, there is always the option to install fireproof boards made from mineral-based wood. Fireproof boards are easy to install, factory manufactured (which ensures a consistent size and strength) and can be attached not just to beams but also columns and decking.
What to consider when managing an intumescent fire protection project
Before project kick-off, there must be a thoughtful and rigorous assessment of structural and environmental conditions. This is key to defining the project scope, and will often help determine what intumescent fire protection method is appropriate. For instance, does the building include any exposed steel or columns? Could there be abrupt environmental changes to consider? Asking these sorts of questions can help identify any complications that may impact project delivery. Below are just some of the factors that should be considered from the outset:
For intumescent coatings to work properly, they must be applied to a surface free of contaminants or debris. This is a common concern in older buildings, which for example may contain traces of lead-based paint. If this is the case, then your project schedule may need to be adjusted to make time for specialist vapour abrasive blasting. This involves the high-pressure projection of a substrate onto a surface and is recommended for removing lead-based paint as it produces much less dust than other blasting methods. If the surface is not adequately prepared, then it is highly likely the intumescent fireproofing will be non-compliant with industry standards. It will also have an impact on any decorative finish, so if aesthetics are a priority it is strongly advised to invest in thorough surface preparation.
On-site or off-site application
This is a particularly important aspect of the project to consider, as it will likely have a significant effect on timescales and may require liaising with additional service vendors. Both options have their benefits and drawbacks. For example, on-site intumescent applications often have fewer up-front costs, and it is easier to ensure that the finished surface blends in seamlessly with the surrounding space. However, off-site applications benefit from taking place in a controlled environment, which means that there would be no problems resulting from accessibility and weather conditions. Off-site application is also heavily supervised, which makes it easier to enact stringent quality control standards in both the level of fire resistance and the quality of finish.
Temperature and ventilation
For intumescent coatings to ‘cure’ properly, there needs to be a consistent temperature and humidity. Therefore, you may need to utilise additional heaters if your team is working in colder conditions. Indirect heaters (rather than combustion source heaters) are recommended as they reduce excess humidity. It is also crucial that there is a consistent airflow, otherwise the intumescent coating may not adhere properly to the surface. It is advised that there are at least 0.3 air changes per hour in the first 72 hours after installation. Therefore, you may need to bring in an additional HVAC system if there is not enough passive ventilation in the immediate area.