Flammable vs. Inflammable - What’s the difference?

19 July 2018

A grammatical odyssey into fire safety standards…

RockWorld imagery, match, fire,

On 23rd May 2018, during her response to the Hackitt report, PM Theresa May inadvertently highlighted one of the key issues related to fire safety in the UK building industry; specifically, the language used to communicate the combustibility of products and materials.

When addressing a question regarding the banning of combustible materials in high-rise buildings, the PM referred to "...The banning of inflammable cladding." This created a talking point in the media regarding the use of the word 'inflammable' to mean 'to catch fire' – The reason? Well, it seems a large portion of the population assumed that 'inflammable' meant 'does not catch fire'.

In English, we think of the prefix 'in-' to mean 'not' e.g. inactive means 'not active', inconclusive means 'not conclusive', inconsiderate means 'not considerate' etc. So, it's totally understandable that many English speakers would believe 'inflammable' meant 'not flammable'.

The word 'inflammable' originates from the Latin verb 'inflammare'; a combination of 'flammare' (to catch fire) and the Latin take on the prefix 'in-' (to cause). So, in this case, 'flammable' and 'inflammable' are synonyms.

Unfortunately, 'inflammable' isn't the only term used in the communication of fire safety standards to cause confusion.

Today more than ever, it is essential that we establish clarity in the language and definitions used in fire safety standards, specifically in regards to building materials like insulation and cladding.

European Reaction to Fire Classification System

The European Reaction to Fire classification system (Euroclasses) is the EU standard for assessing the qualities of building materials in the event of exposure to fire. This standard is a legal requirement for CE marked construction products, and relevant for both the United Kingdom and the Republic of Ireland.

As the name suggests, this classification system assesses and rates the 'reaction to fire' performance of construction products, providing a clear and comprehensive method for comparing the performance of products when exposed to fire.

When products are tested according to the Euroclass system, a range of factors are investigated: ignitability, flame spread, heat release, smoke production and propensity for producing flaming droplets/particles. The Euroclass system is accepted by all European Union States (and is mandatory where there is a Harmonised Product Standard) and includes seven classification levels, from A1 to F.

Understanding the Euroclass classifications is vital to clarifying the terms used by manufacturers.

The Euroclass system states that products achieving A1 classification are defined as non-combustible under these Regulations. Products achieving an A2 classification are recognised as products of limited combustibility, offering “no significant contribution to fire growth”.

Products achieving a rating of B-F are deemed to be combustible.  Where a product has not been measured for fire safety under the Euroclass system, then it will be classed as F, meaning no performance declared (NPD).

The key words here are non-combustible and combustible, which the Oxford English Dictionary describes as…

Non-combustible: Does not burn if exposed to fire.

Combustible: Able to catch fire and burn easily.

These are the legally defined terms within the Building Regulations. Simply, if a material cannot be described as ‘non-combustible’, then it means that it can ‘catch fire and burn easily’.

When we consider the fact that a vast majority of buildings screened and covered by the DCLG (now MHCLG) BS8414 testing program failed to meet current fire safety standards, it becomes clear just how ambiguous, complex and confusing the terminology can be.

The problem is that there are many materials out there that don’t rate highly against the Euroclass standard, so terms that sound like they couldmean non-combustible emerge. Fire safe, fire proof, fire retardant and flame proof are all used to describe product performance but do not define that the product is non-combustible.

Here then is our definitive guide to the terms currently in use, and what they really mean…


Glossary of Terms and Definitions

Non-combustible -  made of material that does not burn if exposed to fire (Oxford English Dictionary)

Combustible - able to catch fire and burn easily (Oxford English Dictionary)

Non-flammable - not capable of burning or not easily set on fire (Oxford English Dictionary)

Inflammable - easily set on fire (Oxford English Dictionary)

Flammable – easily set on fire (Oxford English Dictionary)

Fireproof – able to withstand fire or great heat (Oxford English Dictionary)