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The Flashover Principle

Flashover is the rapid transition to a state of total surface involvement in a fire of all the combustible materials within an enclosure. 
Flashover is characterised by the spontaneous ignition of combustible smoke and/or toxic effluents from a fire, with the smoke acting as the 'conveyor belt' for the rapid change to total surface involvement of all combustible materials, people included.

Flashover can also be described as the moment when fire threatens to leave the room of origin to cause spread of fire into adjacent spaces in an uncontrolled explosive manner. In so doing, it is likely to increase the risk potential for loss of life by a factor of some 300%.

Differentiation of Products by Flashover
The Euroclass system for reaction to fire is based on the tendency of a product to promote the conditions for flashover in a room or enclosure. There are seven Euroclasses from A1 to F - see the table below.

The data from a battery of small/medium scale fire tests is used for the classification process in correlation with a large-scale reference test. Flashover is not measured in the small-scale reaction to fire tests of construction products. It is however measured in the larger Room Corner Test ISO 9705 - the reference test for Euroclasses in the EU reaction to fire classification system. The reference test is also used as the appeal system when there is uncertainty regarding the classification of some contemporary products, or when initial classifications are formally challenged.

EuroclassFlashover in the Room Corner
Reference test
A1No flashover
A2No flashover
BNo flashover
CFlashover between 10 - 20 minutes
DFlashover between 2 to 10 minutes
EFlashover before 2 minutes
FNo data available

Euroclass A1, A2 and B products are much safer in fire than Euroclass C, D and E products. This new classification system indicates the hazard and ensuing risk of flashover. Class E products are likely to be extremely volatile in fire, to produce copious amounts of noxious smoke, to limit escape and to overwhelm any occupants before they can escape. In the case of some lining products, flashover can occur in seconds not minutes, well before the time that any threat is recognised or reacted to in a real life fire.

Products that do not exhibit flashover in the reference test [Euroclass A1, A2 & B] are differentiated and classified on their proximity to non-combustibility and according to their potential heat release rate under specified exposure conditions.