Fire Resistance or Reaction to Fire Testing: Which Fire Test Does Your Product Need?

Fire testing of products has two distinct disciplines, reaction to fire testing and fire resistance testing, and they answer two entirely different questions.

As a UKAS-accredited fire testing laboratory, this is one of the most common points we help manufacturers at the start of their test journey work through. So, here's the distinction, explained through the lens of the fire itself.

The dividing line: flashover

Every compartment fire follows a broadly similar journey: ignition, growth, and, if not controlled, flashover, the point at which the fire transitions from a localised, growing event into a fully developed fire engulfing the entire compartment. After flashover, temperatures rise dramatically and survivability inside that space significantly drops.

That single moment is the cleanest way to separate the two test regimes.

• Reaction to fire testing sits before the point of flashover. It's concerned with how a material behaves during the early growth of a fire – how easily it ignites, how much heat it releases, how quickly flame spreads across its surface, and how much smoke it produces. These characteristics directly affect how fast a fire can grow and whether it reaches flashover in the first place.

  
  

• Fire resistance testing sits after flashover. It assumes a fire is fully developed and asks whether a building element can contain it for a defined period. This can include walls, doors, floors and penetration seals.

  
  

If you’re new to manufacturing, or developing a new product, understanding which side of flashover your product sits on is usually the fastest way to identify which test route applies. This will help you get your product ready to test and ultimately get your product to market faster.

Reaction to fire testing: how a material behaves as a fire grows

Reaction to fire testing examines the combustibility characteristics of a material and its contribution to fire growth and spread. In the UK and Europe, the results feed into a BS EN 13501-1 (Euroclass) classification - the A1 to F scale. You can read more about reaction to fire classifications here.

Since BS 476 reaction to fire testing was withdrawn in the UK in March 2025, BS EN 13501-1 classification is the only available and compliant route for manufacturers.

The specific test method depends on the classification being targeted, but typically includes a combination of the tests listed below:

• Single Burning Item (SBI) test (BS EN 13823): exposes a product to thermal attack from a single burning item to assess flame spread, heat release, and smoke production

• Small flame test (BS EN ISO 11925-2): assesses ignitability under direct flame contact

• Non-combustibility test (BS EN ISO 1182): identifies products that produce negligible heat or flame at high temperature, relevant to the highest Euroclasses

• Gross heat of combustion / calorific value test (BS EN ISO 1716): determines the maximum potential contribution a product could make to a fire

  
  

Reaction to fire testing is the route for surface materials and products whose primary fire risk is contributing to growth and spread - external cladding, insulation, roofing materials, membranes, and wall linings etc.

Fire resistance testing: how a building element performs once fire takes hold

Fire resistance testing measures whether a building element can maintain its function under intense thermal attack for a defined period usually expressed in minutes, from 30 up to 240. Performance is assessed against three criteria, often seen together as an R E I rating:

• R — Load-bearing capacity: does the element continue to carry structural load

• E — Integrity: does it prevent flames and hot gases passing through

• I — Insulation: does it limit temperature rise on the unexposed face, so the next compartment doesn't ignite.

  
  

Products undergoing a fire resistant passive fire protection, the first line of defence protecting escape routes, compartmentation, and structural integrity during a fire. It applies to elements like doorsets and hardware, walls and partitions, glazing systems, penetration seals, and linear joint seals. These are the components that can ensure life safety in an event of a developed fire.

So which test does your product need?

In practice, the question to ask is: what job does this product do in the building, and at what point in the event of a fire does that job matter?

• If your product is a surface, lining, or material whose main fire risk is how it ignites, burns, or contributes to a growing fire, you're almost certainly looking at reaction to fire testing and a BS EN 13501-1 classification.

• If your product is a building element expected to hold a line, physically separating one space from another, while a fire is fully developed, you're looking at fire resistance testing against the relevant BS EN standard for that element type.

  
  

Here’s a side-by-side comparison.

Reaction to Fire Testing	Fire Resistance Testing
Before flashover	After flashover
How does the product contribute to fire?	Can the element contain the fire?
Ignition, flame spread, heat and smoke	Integrity, insulation and load-bearing capacity
Materials and surfaces	Building elements

Ensuring Life Safety

United Kingdom Testing & Certification (UKTC) is a UKAS-accredited fire testing laboratory offering reaction to fire and fire resistance testing for construction & building products. Our testing allows manufacturers to evaluate performance and ensure compliance with regulatory requirements.

If you’re ready to start your next test program, or even if you’re unsure where to start, contact our team by clicking here.