Fire Retardancy

GRP Fire Retardancy

Polyester resins are made up of carbon, hydrogen and oxygen atoms and, like all organic compounds, they will burn. However, by altering their structure and/or the use of additives, it is possible to modify their burning behaviour so that laminates made from such resins present a lower hazard under fire conditions.


In most applications the use of GRP presents no greater fire hazard than the use of a very hard wood. Unfortunately a ‘standard fire’ does not exist and behaviour of GRP in a fire depends on a number of factors amongst which are:

Ease of ignition
Fuel contribution
Fire penetration
Surface spread of flame

The following are brief summaries of some tests used. The appropriate specification should be consulted for full details.


Simple horizontal burning tests

Many tests for fire behaviour exist and almost every country has its own particular methods, often requiring large specimens and special equipment. The following are brief summaries of some tests used. The appropriate specification should be consulted for full details.

Usually a strip of material 150mm x 12.5mm is clamped horizontally and a test flame is applied to one end. 
The material under test may be a cast specimen or a laminate; the test flame can be from a gas or alcohol burner; and the results can be expressed as a burning time, a burning rate or the distance burnt. Tests of this type include:
BS 2782: 1974 Method 508A.
BS 3532: 1962 Appendix B.
British Rail Specification 602. Appendix 9.
Ministry of Technology OTO 5537 & 5549.
A.S.T.M. 0635.

British Standard 476: Part 7: 1971.

Fire tests on building materials and structures

Surface spread of flame test for materials. This test requires complicated equipment. The test specimen 90cm x 22.5cm is cut from the laminate and fixed at right angles to a radiant panel and heated to a prescribed temperature gradient. It is then ignited at the hotter end for 1 minute. The spread of flame along the specimen is recorded until extinction or for 10 minutes. Results are classified as:

Class 1

not more than 165mm

Class 2

not more than 215mm during first 1½ minutes and not more than 455mm after 10 minutes or at extinction

Class 3

not more than 265mm during first 1½ minutes and not more than 710mm after10 minutes

Class 4

exceeding Class 3 limits

British Standard 476: Part 3: 1958. Fire penetration and spread of flame tests

This test also requires complicated equipment. It consists of three parts: a preliminary ignition test, a fire penetration test and a spread of flame test. The specimen is subjected to radiant heat and a vacuum is applied to one side to simulate service conditions. A specified flame is applied to the test piece for various durations and the time for the flame to penetrate, as well as the maximum distance of flame spread, are noted. Glowing, flaming, or dripping on the underside of the specimen are also taken into consideration.
Results are classified as follows: The classification is prefixed by Ext. F or Ext. S according to whether the specimen was tested flat or at an inclined plane. The prefix is followed by two letters, the first showing the result of the penetration test, the second that of the spread of flame test.

British Standard 476: Part 6: 1968: Fire Propagation Test for Materials

In this test, which measures ease of ignition and the rate at which they evolve heat on combustion, specimens 225mm x 225mm are exposed to small gas jets c. 37mm high to radiant heat from electric elements. The hot gases evolved from the specimen are channelled through a chimney and their temperature measured. Comparison is made with a standard non-combustible material (asbestos) and thus temperature differences at specified intervals are converted into rates of temperature rise and integrated to provide an index of performance I. Certain values for I and the sub-index i are specified in the Building Regulations.

A. S. T .M. E84-76 Tunnel Test

This measures the behaviour of laminates which form the roof of a tunnel 7.62m long and 0.51 m wide. The results on flame spread are compared with asbestos cement board (taken as 0) and red oak flooring (taken as 100). Fuel contribution and smoke can also be measured
GRP solutions

Get in touch for a free, no-obligation quote for your latest project

Scroll to Top