Handling Flammable Materials
To handle a flammable substance safely, follow these guides to prevent injuries and accidents.
What is fire?
In essence, a fire or combustion occurs when an oxidising agent (such as oxygen), combustible material (such as fuel) and an ignition source (such as an open flame) are added together. The understanding of the fire chemistry needs to be appreciated in any measure to control fire. Fire is an exothermic (gives off heat) oxidative reaction that can involve solid, liquid or gaseous fuel.
Flaming results from the vaporization of fuels (fuels being heated to the point of giving off gases) and their ignition and subsequent oxidation. It is also important to recognise that not all fires exhibit flaming. Some solids may exhibit smouldering which is glowing combustion on the surface of the material. In addition, combustion that normally occurs in confinement with the subsequent generation of pressure will result in an explosion. For example, flammable gases that are pre-mixed with oxygen upon ignition will expand and result in considerable pressure. If confined, they may explode the container. The combustible material must be heated to its ignition temperature before it will support combustion or the spread of flames.
Burning will continue until the combustible material is consumed or the oxidant is depleted or below the necessary amount for combustion or the heat is removed or prevented from reaching the combustible materials not allowing for fuel vaporization or the flame is chemically inhibited or cooled to stop the oxidation process.
What are the different types of flammable materials?
A flammable material is any liquid, solid or gas that will ignite easily or burn rapidly. Flammable solids can be found in a number of different forms, each of which may exhibit different properties. Example of flammable solid are dusts and powders (flour, cellulose, fine metals); spontaneously ignitable materials (white phosphorus, sodium hydride) and endothermic materials (such as fish meal). As for flammable gases, they can ignite and burn in normal atmospheric concentrations of oxygen (that is room air). Some examples of flammable gases are butane, methane, hydrogen and acetylene. Leakage of compressed or liquefied gases can produce a flammable or explosive atmosphere in a confined space. This is obviously true where the gases themselves are flammable and under high pressure but may also be true in the use of non pressurised liquefied gases. Even relatively safe liquefied gases such as liquid air or liquid nitrogen, if kept in open vessels for too long, will generate concentrations of liquid oxygen which can contribute to an explosion. Proper care with compressed gas cylinders and cryogenic set-ups is essential.
Flammable liquids do not burn; their vapours do. As it is unlikely that air can be excluded and unrealistic (given the constant possibility of a spill) to assume that the vapour concentration can be controlled, the primary safety principle for dealing with flammable liquids is strict control of ignition sources. Ignition sources include electrical equipment, open flames, static electricity, and, in some cases, hot surfaces. Others working in the vicinity should be informed of the presence of flammable substances so that ignition sources can be eliminated. Obviously, it is very important to know which of those sources is capable of igniting a substance that is being used.
How to handle flammable materials?
Remember that most flammable vapours are heavier than air, and will spread out horizontally for considerable distances until an ignition source is contacted. If possible, flammable liquids should be handled only in areas free of ignition sources. Heating should be limited to water and oil baths, heating mantles, and heating tapes. Static-generated sparks can be sudden ignition sources. When transferring flammable liquids in metal equipment, take care that metal lines and vessels are bonded together and grounded to a common ground. Ventilation is very important. A fume hood should be used when flammable liquids are allowed to stand in open containers or are handled in any way.
Two important considerations must be made storing flammable materials; the chemical properties of the material and the proper container to control the potentially hazardous properties. The container of choice must be leak-proof and must control if not prevent the release of flammable vapours. For portable containers, this usually means self-closing or sealed spouts. Initial consideration and planning of the storage location should include the types of materials being stored, the chemical properties of the materials, the area in which storage will occur and the activities or potential activities in the area. In the transportation of flammable materials, a typical symbol being used as a precautionary label is shown in the orange diamond-shaped box.
To handle a flammable substance safely, its flammability characteristics, flash point, upper and lower limits of flammability and ignition requirements must be known. This information usually appears on each chemical fact sheet known as Material Safety Data Sheet (MSDS).