What structural measures can prevent the spread of fire?

Construction projects, be they commercial or residential, must involve fire protection specialists from the outset. This is particularly evident post-Grenfell, and nearly 4 years later investigations continue to unearth examples of non-compliance that are troubling to say the least.

In December 2020, the BBC reported on widespread instances of defective fire safety measures in buildings across England and Wales. One consultant found that out of the 2,000 buildings he inspected, 90% had issues and the majority of these were not related to cladding.

The UK government is taking heed of the issue, having announced the introduction of a new Fire Safety Bill in March 2021 as well as a £16m investment in fire and rescue services. To learn more about this, take a look at our article on fire safety regulations in 2021.

At CLM Fireproofing, we are committed to upholding the highest fire safety standards and sharing our knowledge and experience with building owners and landlords. For instance, while they may be well-versed with solutions such as fire alarms, extinguishers and fire doors, they may not know about some of the structural measures that help reduce the risk of fire – otherwise known as passive fire protection.

In this article, we will be providing an overview of how fire spreads in buildings, before outlining the structural measures that are integral to an effective passive fire protection strategy.

How does fire spread?

Fires start with an ignition, whether it’s a spark from a faulty appliance or an overheated surface. If there is enough oxygen and an ample amount of fuel, it doesn’t take too long until a fire starts. Once this happens, there are three main ways in which a fire can spread:

• Convection – Convection is the most common way fire spreads in a building. As the heat rises from its initial source, the fire travels upwards and spreads horizontally once it hits the ceiling, engulfing everything in its path.
• Conduction – Conduction is the process through which fire spreads via direct contact between combustible materials. One of the main causes of a building collapsing due to fire is the conductibility of structural materials such as steel beams.
• Radiation – We often think of radiation in terms of ‘radioactive’ material, but the term simply refers to the emission of energy in either rays or waves. A large fire will cause heat energy to radiate through a space, causing flammable materials to increase in temperature to the point where it ignites.

How fast does fire spread in a building?

Several factors can affect the speed at which fire spreads in a building. For example, if there is insufficient or damaged compartmentation then smoke and flames can easily move between rooms and floors. We must also consider the presence of flammable or combustible materials. This applies to materials both inside a building and within its external walls. The below timescales are an informed estimate, and should not be used in place of a thorough risk assessment:

• From the first point of ignition, a fire can get out of control in 30 seconds or faster if flammable materials are present.
• Within 1 minute smoke will fill a room, rising to the ceiling and then descending.
• After 3 minutes temperatures can reach over 300 degrees and will begin spreading to other rooms.
• After 5 minutes the heat from the source of the fire will begin to ignite its entire surroundings. This is referred to as a ‘flashover’.

Can a building collapse from fire?

A number of structural elements in a building can be damaged from fire, across a variety of temperatures and speeds. Therefore, a collapse can occur across multiple stages of severity. The most common cause of building collapse is damage to non-structural elements, which then increases the risk of structural exposure to fire. These elements include false chimneys, roof coverings, and windows. For more information, consult the official resources provided by National Operational Guidance titled ‘Hazard – Partial or Structural collapse: Fires in buildings’

What do we mean by structural measures?

The term ‘structural measures’ defines the features of a building that are constructed to serve as part of a fire protection strategy. If a fire were to occur, they help to preserve a building’s structural integrity for as long as possible.

The main purpose of structural fire protection is to prevent fire and smoke from spreading throughout the building. This helps to contain the damage, and ensure there is an ample window for the building’s inhabitants to be safely evacuated. The Building Regulations for England and Wales have provided guidelines for how long a building must maintain its structural stability in the event of a fire:

• A building less than 5 metres tall must remain stable for 30 minutes
• A building between 6 and 18 metres tall must remain stable for 60 minutes
• A building between 19 and 30 metres tall must remain stable for 90 minutes

Below are some examples of structural measures (commonly used in a passive fire protection strategy) that can stop a building from being fully consumed by fire. When implemented correctly, these measures can save lives and reduce financial losses.

Intumescent Coatings

In the event of a fire, steel will lose its load-bearing properties once it reaches a certain temperature (this can vary between 350° and 750°). Therefore, steel structures must be insulated using intumescent paint. This increases the amount of time before the steel collapses, giving firefighters more time to evacuate a building. If you’d like to pursue this subject in further detail, consult our article on how fire affects structural steel.

When exposed to temperatures of up to 250°C, multiple chemical components inside the intumescent coating will react. This causes the coating to increase in density, creating a fireproof layer to protect the steel. These intumescent coatings can be applied in a variety of ways, from thin filming coatings to spray-applied paint.

Intumescent coatings are easy to apply both on and off-site. They are also suitable for not only steel but concrete, timber, and composite elements. As well as this, applying an intumescent coating doesn’t affect the material’s mechanical properties. This means that the coating is essentially ‘neutral’ unless exposed to extreme temperatures. This makes intumescent coatings both an efficient and effective fire protection measure.

Compartmentation

Fire compartmentation involves dividing a building into a series of ‘cells’. These cells are then separated using fire-resistant materials and structures. Fire can quickly engulf a building due in part to the ‘chimney effect’. This is when the airflow between floors and rooms ‘pushes’ flames throughout a structure. Compartmentation reduces this effect, containing the flames and smoke to a specific cell. You can find out more about exactly how this works in our guide to compartmentation.

There are multiple ways to compartmentalise a building, such as fire walls, doors, and cavity barriers. Cavity barriers inhibit the spread of smoke through open spaces in roofs and between floors. These barriers can be made from a variety of materials, such as concrete, gypsum or masonry.

There is no doubt that in principle, compartmentation is an effective way to hinder the spread of fire. However, there are times when compartments can be breached due to building maintenance. This leads to our next structural fire protection measure.

Fire stopping

Sometimes when plumbers, electricians, and contractors work on a building, they can inadvertently compromise structural fire protection measures. Say an electrician drills holes and runs wires through a fire wall. No matter how small this hole may be, the wall no longer offers effective fire protection. Fire can penetrate the smallest gaps and ignite almost anything that lies in its path. Therefore, these gaps must be filled as quickly as possible, and by qualified fire stopping contractors. This process is called ‘fireproofing.’

Successful fireproofing requires the use of specific fire-resistant materials. Any breaches in fire compartments must be filled using an intumescent sealant. when exposed to high temperatures. This fills any gaps and prevents the passage of smoke and flames. Any openings between compartments, such as doors, windows, joints, pipes, and ducts, must be fireproofed. It is vital that in the event of a fire, there is no opportunity for fire to break through a compartment.

Construction professionals must realise that it takes more than investing in structural measures. Firstly, these measures must be implemented in compliance with industry regulations. Secondly, they must be reviewed regularly, with any breaches or material degradation swiftly rectified.

CLM Fireproofing is the UK’s leading provider of passive fire protection solutions. Our structural fire protection contractors have worked on some of the country’s most iconic buildings. All of our work is carried out by highly skilled and dedicated professionals. Every member of the team operates in strict compliance with health and safety regulations.

If you want to learn more about our passive fire protection services, contact our team of experts today.