Contamination Type

Particles/Particulate – Are generic terms used to describe airborne solid or liquid substances in the finely divided state, i.e. particulate aerosols, such as dusts, mists/fog, fumes, fibres, smoke, nanoparticles as well as microorganisms. These may range in size depending on the nature of the substances (e.g. fine powder or granular) or the nature of the process that generated these contaminants. Particles are much larger than individual molecules and their inhalation and damage causing properties depend on physical and chemical characteristics such as size, shape and density. The visibility of particles is a function of many factors including size, concentration and ambient lighting conditions.

Particulates may be

  • Mechanically generated – from grinding, crushing, drilling, sanding and spraying processes
  • Thermally generated – e.g. welding fumes, bushfire smoke. Thermally generated particulates are much smaller than mechanically generated particles. This needs to be taken into account in the selection of respiratory protection.

Dusts – Solid particles generated and dispersed into the air by, for example, handling, crushing, grinding of organic or inorganic materials such as rock, ore, coal, wood and grain.

Mists – Mists are suspended liquid droplets generated by condensation of vapour back to liquid state or by breaking up as a liquid into a dispersed state such as by splashing, spraying or atomising. Mist is the term applied to a finely divided liquid suspended in the atmosphere. Examples are an oil mist produced during cutting and grinding operations, acid mists from electroplating, acid and alkali mists from pickling operations and the condensation of water vapour to form a fog.

Fume – Extremely fine particles, usually less than 1.0 µm in diameter, formed from a volatilized solid that has condensed in cool air. In most cases the hot vapour reacts with air to form an oxide. Fume is often associated with molten metals especially in processes such as welding. At high fume concentrations, agglomeration of particles may result in particles with much larger dimensions.

Fibres – There are many different types of fibres. They can be naturally occurring e.g. asbestos, cotton or man made e.g. man-made vitreous fibres (MMVF), kevlon, carbon fibres. Fibres are generally defined by their aspect ratio, that is the ration of their length to width.

Gas/Vapour

Gases and vapours are both in a gaseous state of matter without fixed shape or volume but differ in their relationship to room temperature. The terms gas and vapour are often used interchangeably in casual conversation, but they have distinct technical meanings based on the substance’s state at room temperature.

  • A gas is a substance that exists in the gaseous state under standard conditions (room temperature and atmospheric pressure). It does not have a definite shape or volume and will expand to fill any container. It exists well above its boiling point (e.g. Oxygen, helium, carbon dioxide)
  • A vapour is the gaseous phase of a substance that is normally a solid or liquid at room temperature (e.g. water vapour, petrol vapours, solvent vapours mercury vapour) and can be condensed back to a liquid/solid by increasing pressure. It exists in equilibrium with its liquid or solid state.

Gas/Vapours may have an Immediately Dangerous to Life or Health (IDLH) level. An IDLH atmosphere that poses an immediate threat to life, would cause irreversible adverse health effects, or would impair an individual’s ability to escape from a hazardous atmosphere

Reference/s for further information and detail: