When it comes to building construction and safety, one of the most critical factors to consider is how materials respond to fire. Insulation, a major component used in buildings for temperature regulation, also plays a significant role in fire safety. Understanding the fire rating scale for insulation can help builders, architects, and homeowners make informed decisions to enhance safety and comply with building regulations. This blog explores the fire rating scale for insulation, discussing its importance, the different types of ratings, and how these affect building safety.
Why is a fire rating important?
Enhanced fire safety
A good fire rating for insulation enhances a building’s overall fire safety. Materials that are resistant to fire can help contain and slow the spread of flames, reducing the risk of fire moving from one part of a building to another. This containment is vital during a fire incident, providing occupants with more time to evacuate safely.
Reduced smoke production
Insulation materials that have a higher fire rating not only resist burning but also produce less smoke when exposed to fire. Smoke is one of the leading causes of harm in fire incidents, as it can obscure vision, hinder breathing, and contain toxic gases that can incapacitate individuals, preventing them from escaping. By using insulation with a low smoke production rating, the air quality is better preserved in the event of a fire, enhancing the chances of a safe evacuation.
Prevention of fire spread
Insulation is often used throughout buildings, running through walls, floors, and ceilings. Insulation that is not fire-resistant can act as a fuel source, significantly accelerating fire spread throughout the structure. Fire-rated insulation materials are designed to not only withstand heat but also to prevent the spread of fire. This is crucial in high-rise buildings, hospitals, schools, and other large structures where evacuating people safely can take more time.
Compliance with building codes
Building codes and regulations often mandate specific fire ratings for insulation based on the type of construction and its intended use. These regulations are designed to ensure that all buildings meet a minimum standard for fire safety, which is particularly important in densely populated areas or buildings with vulnerable populations. Using the correct fire-rated insulation is necessary to comply with these regulations and avoid legal repercussions.
Insurance requirements
Insurance companies may require that buildings use materials that meet specific fire safety standards, including fire-rated insulation, to reduce risks. Compliance with these requirements can affect insurance premiums, liability, and coverage scope, especially in commercial properties. In the event of a fire, having the correct fire-rated insulation can affect the outcome of insurance claims related to fire damage.
Long-term building integrity
Buildings that incorporate high-standard fire-rated insulation are more likely to maintain structural integrity in the event of a fire. This not only helps in potentially saving lives during the incident but also preserves the building’s framework, leading to potentially lower restoration costs post-fire.
The fire rating scale
The fire rating of insulation materials is generally determined through specific tests that measure flame spread and smoke-developed indices.
- The Flame Spread Index (FSI) measures how fast and far flames spread along the surface of the insulation during the first ten minutes of a test. The lower the FSI, the better the material resists fire spread.
- Smoke Developed Index (SDI) assesses the amount of smoke a material produces when it burns. Similar to the FSI, a lower SDI is preferable as it indicates less smoke production, which is vital for visibility and toxicity levels during a fire.
Categorising ratings
Class A (or Class 0 in the UK)
- Flame Spread Index (FSI): 0-25
- Smoke Developed Index (SDI): Less than or equal to 450
Class A or Class 0 materials have the highest resistance to fire. They are designed to be non-combustible, meaning they do not contribute significantly to a fire’s fuel load. These materials are ideal for use in areas where the risk of fire is higher, such as commercial kitchens, public theatres, or buildings with heavy electrical equipment. They are also often required in external cladding and roofing in both residential and commercial buildings.
Class B
- Flame Spread Index (FSI): 26-75
- Smoke Developed Index (SDI): Less than or equal to 450
Class B materials have a moderate resistance to fire. They are typically used in places with a lesser likelihood of severe fire exposure but where a good level of fire resistance is still necessary. This rating is common for interior walls and ceilings in residential and commercial buildings.
Class C
- Flame Spread Index (FSI): 76-200
- Smoke Developed Index (SDI): Less than or equal to 450
Class C insulation materials offer basic protection and are suitable for areas with a lower risk of fire exposure. They are often used in residential settings where regulations may not require higher-rated materials. This class is adequate for parts of buildings that are less likely to be sources or accelerators of a fire.
Class D, E, and F (European Standards)
- These classes indicate progressively lower degrees of fire resistance.
- Not commonly used in direct comparison to U.S. standards but important in European contexts.
These classes are less resistant to fire than Classes A, B, and C and are used less frequently in critical areas of construction. They may be suitable for applications where other fire prevention measures are in place or where the risk of fire is minimal.
How do different insulation materials measure up?
Mineral wool (including rock and glass wool) is naturally non-combustible and typically achieves a Class A fire rating. This makes it an excellent choice for fire safety as it does not contribute to the spread of flames or produce significant amounts of toxic smoke. Mineral wool can withstand temperatures up to about 1000°C, making it highly effective in preventing fire spread. The reason for mineral wool resisting fire so well is the composition. Most mineral wool products are produced from volcanic rock, which is naturally extremely temperature-resistant. The rock is melted into fibres and then spun into large batts that form the boards.
Source: Rockwool YouTube
EPS is a type of foam insulation that, in its basic form, is not highly fire-resistant. Standard EPS usually falls into Class E under European standards, indicating a higher flammability. However, fire-retardant grades of EPS are available that perform better and can reach Class B ratings. These are treated with fire-retardant substances to reduce flammability.
Kingspan K5 is an insulation board used primarily for external insulation systems. It is made of phenolic foam, which offers superior fire performance compared to many foam insulations. Under the UK building regulations, Kingspan K5 generally achieves a Class 0 rating, corresponding to a high level of fire resistance. It is classified as having low flame spread and low smoke production.
Wood fibre insulation generally has lower fire resistance than mineral wool or phenolic foams. Untreated wood fibre can be quite flammable; however, it is often treated with fire retardants to improve its fire resistance. Typically, treated wood fibre insulation can achieve Class E or Class D ratings, making it less suitable for high-risk areas unless additional protective measures are taken.
