Assessing fire performance of building materials post-Grenfell

Construction-site

The tragic impact of building fires has meant that since Grenfell the performance of building materials has been under focus. Construction materials have a significant impact on fire spread. They can influence loss of life and property. Also, consequential risk improvements can be difficult and costly to implement.

To put this into context we need to understand how the field of construction materials has evolved over the last few decades and why choosing the right construction materials matters so much. It is critical to make the right choice from the beginning.

As a property insurer, with long experience of mitigating against and dealing with the aftermath of building fires, AIG’s credo is COPE, which stands for Construction, Occupancy, Protection and Exposure. It means we assess the transferred risk from these four angles.

Construction details the fabric of the building: the structure (columns and beams), frame, walls, roof, and insulation. It also includes what can be added on top of or on the side of a building, such as solar panels, green roofs and cladding. Construction also relates to the building’s fire strategy and fire compartmentation. Compartments must be able to contain the fire for the duration they are built for.

Occupancy is related to the activities carried out inside the building, because the hazards induced by human activities are not the same in a library, a school or a social housing block.

Protection relates to how the activities’ hazards and exposure risk are identified, mitigated and dealt with. It includes management procedures like hot work permits, automatic sprinkler protection adequacy, training with the public fire brigade and emergency response plans.

Exposure is about external factors, the neighbourhood and surroundings, and their impact on the building. For example, is it in a floodplain?

Or is it a unit, part of a larger complex? Does it have adjoining properties? Are there sub-tenants in the building?

However, whether a project is a refurbishment, an extension or a new building, testing or choosing the right construction materials may not be simple.

Differences in construction materials can have a significant impact on the spread of fire in the event of a blaze.

If you get it wrong, implementing retrospective risk improvements can be difficult and costly. It is it critical to make the right choices at the beginning. However, this process is considerably more complex than simply selecting between construction materials that are classified as combustible, or non- combustible

Implementing retrospective risk improvements can be difficult and costly

Compliance and classification

As you might expect, this is an area that has become heavily regulated. Legislators in different countries have worked with their construction industries to develop a significant variety of test standards to assess fire behaviour and the properties of construction materials. Confusingly, they are not all equivalent; local regulation may not recognise them all and will vary from country to country.

For example, there is a set of European fire test and classification standards that attempt to harmonise the different codes of construction across Europe. However, these standards do not impose any minimum requirements, which are determined by regulations in individual countries.

In addition, a property insurer may have a view based on claims and losses experience.

There are several different classification methods to choose from, but AIG uses ISO classifications, ranging from 1 (highly combustible) to 6 (fire-resistive):

  • ISO 1 Frame Construction
    Combustible walls, floors, roofs, cladding, usually made of wood, but can contain masonry veneer in a thin layer or metal clad as wood support. Contains metal sheathed with combustible insulation and non-approved expanded plastic foams.
  • ISO 2 Joisted Masonry Construction
    Masonry exterior walls, non-combustible external cladding, but combustible floors and roofs with heavy timber. Often referred to as traditional construction and encountered in many historic buildings.
  • ISO 3 Light Non-Combustible
    No wood. Erected with slow burning material but presents a high risk of collapse due to exposed structural steel.
  • ISO 4 Masonry Non-Combustible
    Masonry exterior walls, one-hour fire resistive construction, slow burning floors, roofs, use of Factory Mutual (FM)1 or the Loss Prevention Council Board (LPCB)2 approved deck roof components.
  • ISO 5 Modified Fire Resistive / Protected steel frame
    Masonry exterior walls, floor and roof, one-hour fire resistive construction, four-inch concrete roof deck and exterior walls minimum.
  • ISO 6 Fire Resistive
    Hollow masonry walls 12-inch-thick, two-hours fire- resistive rating, concrete columns and beams.

Unfortunately, it is often challenging for an insurer to classify a building, due to the addition of extensions and refurbishments.

Considerations

New construction materials often come onto the market with promises regarding energy efficiency and savings, offering a lighter structure, being easier to handle and install, or providing a better resistance to moisture. However, they may also come with hidden hazards, as these elements are used for insulation and are therefore concealed. They may ignite easily, burn quickly, have a higher rate of heat release, produce a large amount of smoke, and generate toxic gases when burning.  They may also increase the potential for rapid fire spread and wall delamination and are potentially more susceptible to wind or water damage.

Fire doors, fire damper and fire stopping have to be designed with the same rating as the fire wall they are mounted on, and with an approved fire rating

The quality of internal fire compartmentation also plays a role in the construction quality and how it will behave in a fire. Fire walls and fire doors are erected to limit the spread of fire. Their duration is dependent on the physical properties of the material, their thickness, and the heat exposure in the fire. They can be compromised easily by openings (like ductwork and cable trays) or if wedged open. A robust management programme can address the latter, but the former needs to be addressed at the design stage. Fire doors, fire damper and fire stopping have to be designed with the same rating as the fire wall they are mounted on, and with an approved fire rating.

Ultimately, the choice of a construction material will not be made solely on the basis of the implications for fire safety. Additional considerations will include, for example, energy efficiency requirements and whether or not the material is considered to be environmentally friendly.

Whatever decision is made will have an impact on the building’s sustainability and life span. It will also impact on the insurance programme regarding the transferability of an asset, the provisional loss estimates, and rate and price calculation at the location level.

Insurers have specialist risk engineers who can assist in the choice of construction materials and help find satisfactory, bespoke solutions. 

It is often challenging for an insurer to classify a building due to the addition of extensions and refurbishments

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