Building codes impose rather rigid restrictions on the use of wood in housing and construction. Both timber and wood-derived products react in varying ways to fire, depending on species but also on the size and form of the product. Furthermore, methods of treatment are employed today on a commercial scale that render wood products resistant to fire to the extent that they will not burn except when directly subjected to an external source of heat, and they cease to burn or glow as this source is removed. There is therefore now much reviewing and rewriting of building codes with respect to fire hazard. Codes should be based on the actual performance of a specific material and any requirement that a material should have particular inherent properties is not consistent with modern technological methods available for protective treatment of materials. This was the view expressed by the experts attending the Fourth FAO Conference on Wood Technology at Madrid earlier this year.
The exceptional fire resistance of heavy timbers is a well established fact. Less known are the possibilities that exist to improve the fire resistance of wood structures by adequate design and planning. Two examples will illustrate such possibilities. In Canada, the fire insurance losses in wood frame houses are lower than in other dwellings. This is due to the appropriate design of frame houses and has been recognized by a reduction in insurance rates. The second example refers to the fire resistance of wooden doors. A few years ago wooden doors manufactured in the Netherlands had a maximum fire resistance of 10 minutes in a standard test. Today, Dutch manufacturers are able to produce wooden doors with a resistance of 40 to 60 minutes.
There are thus considerable possibilities for improvements of the behavior of wood and its products in relationship to fire. To further such improvements, satisfactory test methods must be developed. The growing importance of fire research and fire test methods has been acknowledged for some time. Many factors affect the progress of actual fires in buildings and structures and the difficulty of simulating all of them in a single controlled test is the main reason why a number of different test methods are used to get information on various specific aspects of fire behavior.
At the Madrid Conference on Wood Technology, it was emphasized that any method of fire testing should lend itself to the evaluation of the behavior of all types of materials during a fire and that there was no need to develop specific methods for wood and wood-base material except possibly in cases where research in the development of improvements in fire protective treatments were involved.
There is immediate need for a test which does not require extensive space and expensive auxiliary equipment. Three lines of approach in the development of testing equipment are discernible. They are:
(a) tunnel tests;
(b) box tests;
(c) radiation panel tests.
No preference is given to any one of these methods.
In evaluating the results of a test, it was recognized that reaction to fire cannot be expressed by only one index. While building authorities may wish to resort to simplified expressions, it is not sufficient for research purposes to grade materials in such a manner. It is therefore necessary to report all pertinent measurements, such as ignitability, spread of flame, fire penetration, heat producted by combustion, smoke intensity and others.
This does not exclude the differentiation of materials in classes, whether such grading be done by calculating indices from certain measurements or by setting limits inside which temperature curves should fall. Such grading should apply to all types of material which constitute the fire load in a room or building, that is, furniture, curtains, rugs and other contents. The testing apparatus should be adaptable for testing also such materials.
The ultimate aim is to reduce the number of tests to a select few which could be given international recognition. This is not possible at the present time in the opinion of most experts, who recommend that emphasis should rather be placed on insuring that test methods are directed towards a realistic appraisal of fire hazards.
This is the fiftieth issue of Unasylva
Maps showing, respectively, the political divisions and the incidence of loess erosion in China. All illustrations for this article are used by courtesy of the Chinese Ministry for Water Conservation.
Figure 1. China: Political division
