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Malignant. As applied to a tumor. Cancerous and capable of undergoing metastasis, or invasion of surrounding tissue.

Manual of Tests and Criteria. Manual of Tests and Criteria means the United Nations publication entitled “Recommendations of the Transport of Dangerous Goods, Manual of Tests and Criteria” as amended.

Maximum capacity. Maximum capacity as used in 6.1.4 of IMDG Code (2004 Edition) means the maximum inner volume of receptacles or packagings expressed in litres.

Maximum net mass. The maximum net mass of contents in a single packaging or maximum combined mass of inner packagings and the contents thereof expressed in Kilograms.

Meter. A metric unit of length, equal to about 39 inches.

Micron (micrometer, m). A unit of length equal to one millionth of a meter, approximately 1/25,000 of an inch.

Milligram (mg). A unit of weight in the metric system. One thousand milligrams equals one gram.

Milligrams per cubic meter (mg/m3). Unit used to measure air concentrations of dusts, gases, mists, and fumes.

Milliliter (mL). A metric unit used to measure volume. One milliliter equals one cubic centimeter.

Millimeter of mercury (mmHg). The unit of pressure equal to the pressure exerted by a column of liquid mercury one millimeter high at a standard temperature.

Mists. Suspended liquid droplets generated by condensation from the gaseous to the liquid state or by breaking up a liquid into a dispersed state, such as by splashing, foaming, or atomizing. Mist is formed when a finely divided liquid is suspended in air.

MSDS. Material Safety Data Sheet.

MSHA. Mine Safety and Health Administration, US Department of Labor.

Mucous membranes. Lining of the hollow organs of the body, notably the nose, mouth, stomach, intestines, bronchial tubes, and urinary tract.