Friability (the condition of being friable) is the ability of a solid substance to be reduced to smaller pieces with little effort. The opposite of friable is indurated.
Substances designated as being hazardous, such as asbestos or crystalline silica are often referred to as being friable if they are present in such a state that small particles easily can become dislodged, thus enabling them to become respirable (able to enter human lungs), posing a health hazard.
Tougher substances, such as concrete, may also be mechanically ground down and reduced to finely divided mineral dust. However, such substances are not generally considered friable because of the degree of difficulty involved in breaking the substance's chemical bonds through mechanical means. Some substances, such as polyurethane foams, show an increase in friability with exposure to ultraviolet radiation as present in sunlight.
A friable substance is any substance that can be reduced to fibers or finer particles by the action of a small pressure or friction, such as inadvertently brushing up against the substance. The term could also apply to any material that exhibits these properties, such as:
- Ionically bound substances that are less than 1 kg/L in density
- Clumps of dried clay
- Mineral fibers
- Polyurethane (foam)
Friability testing is a laboratory technique used by the pharmaceutical industry to test the likelihood of a tablet breaking into smaller pieces during transit. It involves repeatedly dropping a sample of tablets over a fixed time, using a rotating wheel with a baffle, and afterwards checking whether any tablets are broken, and what percentage of the initial mass of the tablets has been chipped off. A typical specification will allow a certain percentage to be lost by chipping, and will not allow any broken tablets.
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