Waste materials have widely varying properties and as a result, the hazards and problems presented in disposal also vary widely.

Solid wastes are normally of lower hazard than liquids or gases, since they are less subject to spills and propagation by flowing or blowing. Solid materials that are noncombustible and stable have little fire or explosion hazard. The most severe hazard exists if solid waste materials are in the form of a combustible dust, or if the material can react with air or water to produce a combustible gas or a highly exothermic reaction.

Inorganic liquids are usually water or water solutions of chemicals such as acids, bases, or salts. Waste liquids are usually dilute solutions, but processes can lead to concentration of hazardous materials through evaporation or phase separation of immiscible liquids or settlement of solids in suspension. For example, water or water solutions can be contaminated with insoluble flammable chemicals, usually floating on top, such as water that has been used in fighting a flammable liquid fire.

The most severe hazards involving inorganic liquids are flammable liquid contamination with associated fire or vapor explosion hazard, and acid solutions which can sometimes react with metals, generating hydrogen in unvented spaces.

Highly reactive liquefied gases such as chlorine or oxygen can present hazards in disposal, especially if contaminated with organic material. Most organic liquids are flammable. In the processing and disposal of waste flammable liquids, the same hazards are found and the same basic safeguards must be followed as in other flammable liquid processes.

In the routine disposal of organic liquids, the process can be safely designed. In a spill of an organic liquid, control and disposal measures must be anticipated in advance and provided for. Most inorganic gases are nonflammable. The main hazards are toxicity and corrosive chemical action, although high concentrations of some gases, such as chlorine and oxygen, can intensify combustion. Organic gases are mainly flammable gases or vapors of volatile liquids. Waste gases may be produced routinely and disposed of. They may be released by operation of venting devices on process equipment, or by a leak in piping or process vessels.

The primary hazards of flammable gases are the ignition of an accumulation of gases within the explosive range, or the burning of an uncontrolled release of gases with exposure to other facilities.

Waste byproducts are normally removed from processes through piping or ducts. Flammable liquids, gases, combustible dusts, and hazardously reactive or damaging chemicals must be kept confined. Materials must be drained or directed to a safe location.

Liquid spills from storage tanks or process equipment are normally confined by dikes or curbs, and directed into drainage systems where they are conducted through piping, channels, or ditches to a point of disposal, process equipment, or a temporary storage facility.

Where the spilled liquid constitutes a fire or explosion hazard, the drainage system is designed to remove the material to a safe location, along a route where it will not expose other facilities. Traps are normally provided so that fire will not be transported while the fuel is removed. The system must be designed to handle runoff of water used in fire fighting and natural water drainage, in addition to possible liquid spills.

Waste materials often become mixed with air as part of a production process. Since air must be returned to the environment, waste materials must be removed, diluted to a safe level, or converted into a form not harmful to the environment. Separation or dilution is normally a physical process, while conversion is normally a chemical process.

After waste materials have been collected and separated as necessary, they must be disposed of, either into the air, water, or ground, or they must be hauled or piped away for disposal by others. Disposal into the air is accomplished mainly by stacks or chimneys. One method is by use of a high stack. Stacks and chimneys, like other high structures, are subject to damage by fire, explosion, wind, lightning, vehicle impact, and collapse.

Disposal into the water is through discharge pipes of varying size and location. The pipes are not subject to damage any more than other objects or structures at similar locations. Disposal into the ground can be done by injection of liquids into deep wells or by burying in sanitary landfills.

The primary hazard is fire involving storage aboveground awaiting burial or involving material inadequately covered. Although the value of such material is slight, there may be exposure to important facilities. The cost of fighting a smoldering underground fire or interruption to use of the burial facility may be significant. FSM