Caution on roof insulation fire ratings

Rigid PIC foam board insulation showed no ignition throughout the Firelab testWhile the new SANS 428 fire regulations, as part of the National Building Regulations, have been welcomed as a major step forward with regard to the testing, evaluation and recommendation of roof insulation materials, D&D Roof Insulation has highlighted a critical shortcoming with the new fire rating system.

The new standard for the evaluation of roof insulation liners comprises various numbered parts which make up the total test protocol procedure. The most important of these is the Part 11 large scale test done at Firelab, with and without sprinkler systems. The test involves the test roof insulation liner being installed, as it is in practice, but in a scientifically controlled environment. The test simulates a scenario where the fire starts small and grows up to roof height.

The completed evaluation of the test product is then rated according to the SANS 428 classification table, in which one of the classifications is Surface Fire Properties. This relates to the flame spread of the material under the test conditions, with 1 being the best (no flame spread) and 6 being the worst (rapid flame spread).

Another aspect of the rating is combustibility, with an ‘A’ classification for non-combustible and a ‘B’ classification for combustible materials. A product would achieve an A1 rating if it did not ignite even in the Part 11 test.

There is however a major shortcoming in the final ratings of roof insulation products.

In June last year, the Part 5 combustibility test parameters were changed in line with international standards, such that even the products previously ‘A’ rated are now ‘B’ rated. D&D Roof Insulation points out that this change was made without due consideration for the effect it would have on the final ratings of materials within the parameters of the SANS 428 test protocol.

The Part 5 combustibility test is done in an electrically heated furnace pre-set at 750°C and the test sample, to be considered non-combustible, should not increase the furnace temperature by more than 50°C or support flaming for more than five seconds.

The fire source in the large scale Part 11 test peaks at around 550°C and any combustible roof insulation material, installed as in practice, will ignite at this temperature. The problem is that products that did not ignite at this temperature at all, as opposed to those that did in the Part 11 test, are all now assigned the same fire rating.

Considering that tin will melt at 233°C, aluminium at 660°C, and steel alloys at around 1 370°C, it is clear that all commercially rated roof insulation materials will be literally obliterated in seconds at 750°C, in the Part 5 test used to rate products’ combustibility.

TIASA – the Thermal Insulation Association of Southern Africa – has taken up this concern with the SABS fire committee and has requested a review of the Surface Flame Spread ratings of roof insulation liners. The review is pending, awaiting the completion of relevant research.

Professionals and contractors are therefore advised to scrutinise SANS 428 test reports of various roof insulation materials closely, before deciding on which product best suits the given application.

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