Chemicals

Knowledge of the hazardous parameters of chemicals is one of the basic conditions of safe working. The preventive measures and requirements for protection against fire may be elaborated only if the physical and chemical properties connected with fire hazard are taken into consideration. Of these properties, the most important ones are the following: combustibility; ignitability; ability to react with other materials, water or air; inclination to corrosion; toxicity; and radioactivity. Information on the properties of chemicals can be obtained from the technical data sheets issued by manufacturers and from the manuals and handbooks containing the data of hazardous chemicals. These provide users with information not only about the general technical features of materials, but also about the actual values of hazard parameters (decomposition temperature, ignition temperature, limit concentrations of combustion, etc.), their special behaviour, requirements for storage and fire-fighting, as well as recommendations for first aid and medical therapy.

The toxicity of chemicals, as potential fire hazard, may act in two ways. First, the high toxicity of certain chemicals themselves, may be hazardous in a fire. Second, their presence within the fire zone may effectively restrict fire-fighting operations. The oxidizing agents (nitrates, chlorates, inorganic peroxides, permanganates, etc.), even if they themselves are non-combustible, largely contribute to the ignition of combustible materials and to their intensive, occasionally explosive burning. The group of unstable materials includes the chemicals (acetaldehyde, ethylene oxide, organic peroxides, hydrogen cyanide, vinyl chloride) which polymerize or decompose in violent exothermic reactions spontaneously or very easily. The materials sensitive to water and air are extremely dangerous. These materials (oxides, hydroxides, hydrides, anhydrides, alkali metals, phosphorus, etc.) interact with the water and air that are always present in the normal atmosphere, and start reactions accompanied by very high heat generation. If they are combustible materials, they will come to spontaneous ignition. However, the combustible components that initiate the burning may possibly explode and spread to the combustible materials in the surrounding area.

The majority of corrosive materials (inorganic acids—sulphuric acid, nitric acid, perchloric acid, etc.—and halogens —fluorine, chlorine, bromine, iodine) are strong oxidizing agents, but at the same time they have very strong destructive effects on living tissues, and therefore special measures have to be taken for fire-fighting.

The dangerous characteristic of radioactive elements and compounds is increased by the fact that the radiation emitted by them may be harmful in several ways, besides that such materials may be fire hazards themselves. If in a fire the structural containment of the radioactive objects involved becomes damaged, γ-radiating materials might be released. They can have a very strong ionizing effect, and are capable of the fatal destruction of living organisms. Nuclear accidents can be accompanied by fires, the decomposition products of which bind radioactive (α-and β-radiating) contaminants by adsorption. These may cause permanent injuries to the persons taking part in rescue operations if they penetrate into their bodies. Such materials are extremely dangerous, because the persons affected do not perceive any radiation by their sensing organs, and their general state of health does not seem to be any worse. It is obvious that if radioactive materials burn, the radioactivity of the site, the decomposition products and the water used for fire-fighting should be kept under constant observation by means of radioactive signalling devices. The knowledge of these factors has to be taken into account for the strategy of intervention and all additional operations. The buildings for handling and storing radioactive materials as well as for their technological use need to be built of non-combustible materials of high fire resistance. At the same time, high-quality, automatic equipment for detecting, signalling and extinguishing a fire should be provided.