Smoke is the end product of combustion. Its composition varies greatly, depending on the material being burned.

The black soot that gives smoke its distinctive colour is quite often carbon. It is produced from the burning of wood, plastic, petroleum, and other organic products. As carbon conducts electricity, it can cause short circuits in electrical and electronic equipment; furthermore, it can cause overheating problems, in heat producing equipment, due to carbon's heat-insulating properties. Carbon does not dissolve in water or solvents and must be removed by mechanical means, such as: wiping, scrubbing and vacuuming.

Sulphate and nitrate are contaminants that are also commonly found in smoke. They are produced from the burning of rubber, lacquer paint, and fuel oil including diesel fuel. Combined with moisture, sulphate and nitrate have the possibility of developing into various forms of sulphurous and nitrous acids. These acids will cause corrosion in metals and electrical contacts, and the corrosive action will accelerate thousands of times upon the application of electricity.

The most harmful substance, often found in smoke, is chloride. It is produced by the combustion of PVC plastic, which is commonly used in insulated electrical wires, plastic sheets, and containers. Chloride reacts readily with moisture and turns into various forms of highly corrosive hydrochlorous acids. In a typical fire scene, the bright orange flash rust found on bare metal surfaces and the yellowing of enamel finish on appliances, are their signatures.

Similar problems occur in cases of chemical contaminations such as: the release of acid fumes, discharge of dry chemical fire extinguishers, etc. It is the water-soluble components in the contaminants that react with moisture and cause corrosion problems.

Pure water is perhaps the least harmful material in the world. It evaporates without a trace. It does not corrode ordinary metals such as iron and copper, and it doesn't even conduct electricity. This can be proved by completely immersing a nail in a very clean glass of distilled water. It will not rust no matter how long it is left there. When distilled water dries there is no residue left behind. Pure water is nothing but straight H2O, just as your old chemistry teacher used to say in class.

What causes water damage are the same substances that make water conduct electricity, the minerals and other deposits that are in it. Tap water carries a certain amount of minerals, such as: calcium, sodium, and magnesium, originating from mineral latent rocks buried deep underground in the water table. Rain water "typically" contains a weak carbonic acid, which originates from dissolved carbon dioxide. It also accumulates more harmful acids from pollutants, such as: sulphur dioxide and nitrous oxides, which are commonly found in polluted air. When rain water enters the ground, all the acids and pollutants enter the ground with it and react with whatever minerals they encounter. When it reaches the water table and re-emerges, it contains a lot more than just H2O. Also, when water passes through the pumping station and all the pipe lines therafter, it picks up metals along the way and the longer it remains in the pipe, the more metals it picks up. Therefore, by the time the water from a broken sprinkler pipe reaches the equipment, it often carries many surprises.

The most harmful thing water does is introduce acids, minerals, and dirt into the equipment. In the presence of water, such contaminants will break down into various ions and start to corrode as soon as they make contact. If the equipment is switched on, while it is still wet, the ions released by the minerals will act as an electrolyte and inevitably cause short circuits. Also, the corrosion process will accelerate many thousands of times under the influence of electricity. Catastrophic failures can occur within minutes or seconds of flipping the switch.

After the water dries, those ions will re-combine into mineral molecules and will stay behind and remain inert. If they are not removed, they will slowly react with moisture in the air, re-activate, continue to corrode and eventually cause the equipment to fail.

Moisture exposure is a costly, and often, an overlooked hazard to electronic equipment. Especially in cases where the equipment has been accumulating dust in the interior due to air convection or mechanical cooling by fans. When air becomes humid, dust particles begin to absorb moisture and they collapse together and form a wet, dense mass. If the equipment is switched on, this wet, dense mass will cause short circuits. If the moisture is allowed to dry, the caking of dust particles will act as heat insulation and will not allow the equipment to cool down properly. This, in turn, may cause overheating and may eventually cause premature failures even though the equipment has never been in direct contact with water.