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Reprinted from The Journal of the Institute of Maintenance and Building Management, Nov 1999

Paint Finishes - Flaming Hazard?

by
DR. PETER LAKE
B.Sc.(Hons), Ph.D., C.Chem., MRSC, MIFS
Summary
It is the responsibility of building owners to ensure that redecoration of communal areas and escape routes does not introduce the additional fire hazards that are now known to arise from multilayer paint. This article briefly outlines the problem and its solutions. It reports that site survey tests are available to assess the fire risk. Independent experience from these indicates that expensive stripping or upgrade coating are only necessary in a minority of cases.
Uncovering the Problem
It is now clearly established that the fire performances of wall and ceiling surfaces required to be Class 0 by Building Regulations can, and often are, adversely affected by overpainting. Recent research sponsored by the DOE(1) confirms that multiple layers of 'Class 1' designated paints may give rise to a Class 4 surface spread of flame even when used on plaster or other non-combustible substrates. Such a performance constitutes a serious fire hazard, unacceptable in communal areas and escape routes. This deterioration is exacerbated by ageing between coats; exactly as happens in routine maintenance decoration.

There is growing evidence that the research findings are reflected in real fire situations. Official investigations into several fire incidents have concluded that multilayered paint surfaces were major contributory factors to the cause and rapidity of fire spread. Several fatalities have resulted in the common access areas of both high rise and low rise apartment blocks, where total casualties average around 250 per year(2).
Understanding the Reasons
All paint (including water-based emulsions) contains combustible material which will spread flame to a greater or lesser extent depending upon the type. When applied to a new substrate it adheres well and in a fire will be difficult to ignite as the substrate conducts heat away from the surface preventing the paint reaching its ignition temperature. As more layers are added the quantity of combustible material increases and the quality of adhesion both to the substrate and between layers reduces. This is aggravated if there has been indifferent surface preparation between coats. Under the influence of heat the paint can blister, particularly if the adhesion is poor, to release flammable gases. Once this happens delamination occurs and, with the substrate no longer in contact, the paint quickly ignites and spreads flame.

The spread of flame classification quoted by the paint manufacturers for their standard products usually refer to British Standard tests(3) conducted on 1-2 topcoat - undercoat finishes on plasterboard. Not surprisingly such results may not apply after further painting. There are however a number of paints available that have been successfully tested at greater coating thicknesses. These may be used up to the tested thicknesses but should not be confused with products that claim to 'upgrade' existing finishes, which are discussed later.
Assessing the Right Solutions
Knowing that there may be a problem in general is not the same as knowing there is one in particular. Building owners would therefore be well advised to evaluate the individual position in each premises rather than bow to pressures to automatically use expensive specialist treatments. Several site survey test methods have been developed to assess the paint fire risk in individual buildings. Typically they are based on microscopic analysis of the type and thickness of the constituent paint layers and on-site measurements of the adhesion and heat exposure behaviour. The data obtained is used as the basis for expert assessment of the level of fire risk and, thereby to establish the correct solution.

Essentially, there are three outcomes of such assessments. On surfaces found to present a high risk or where there is poor adhesion chemical stripping will be recommended. Costs commonly range from 20 - 25 per m2.

Where adhesion is satisfactory, 'upgrade' coatings can be used to improve the fire performance of high risk surfaces. There are several products on the market, falling into two broad categories :- thick coat siliceous formulations and thin coat paints containing fire-retardant additives. Manufacturers should be asked to provide documentation validating that the product achieves a Class 1 surface spread of flame when used over a Class 4 painted substrate. Costs are generally in the range 10 - 20 per m2.

Finally, the assessment may conclude that the fire risk is low, in which case standard emulsions can be used in overpainting. In this connection it is worth noting that it has been the experience of the author and of independent assessment bodies that stripping or upgrading are each necessary in under 20% of cases. By contrast, assessments conducted by stripping or paint companies tend to reveal a much greater need for one or other solution.
Responsibility and Action
Recent legislation, such as the Construction (Design and Management) Regulations and the Fire Precautions (Workplace) Regulations, is progressively placing greater responsibility on building specifiers, owners and clients to ensure the fire safety of the occupants of premises. It is they, not the fire authorities, who must assess the on-going risks and it is they who will be held liable should this not be done.

Those responsible should require that fire risk assessment surveys are conducted on the communal areas of premises involving multilayer paint finishes. These should be undertaken by independent expert bodies prior to further decoration on a representative audit basis. By implementing the resulting recommendations, not only will owners be able to demonstrate that they have discharged their statutory responsibilities, they will have done so in a cost effective manner. Most importantly the fire safety of occupants will have been preserved.

References :-
  1. DETP (DOE) Research Project 39/3/204 : 1994-7
  2. Home Office, UK Fire Statistics 1989 -91
  3. BS 476: Part7: 1987 (1997) Method for classification of the surface spread of flame of product