Smoke is an aerosol that is dispersed in microscopic form and consists of exhaust gases, dust particles and droplets of water vapour. It is usually released through the process of combustion. Smoke is always a mixture of solid and gaseous substances.

The exhaust gases from industrial plants are often called flue gases. The dreaded smoke poisoning can occur in apartment fires or through exhaust gases in unventilated rooms.

Firefighters and rescue teams are also confronted with smoke and must therefore first protect their own lives with supplied air respirators. In extreme situations smoke- or rescue hoods can help when employees need to get themselves to safety.

A vapour is defined as a gas that is generally still in contact with the liquid or solid state from which it has occurred through evaporation.

Over time, a dynamic balance is achieved in which exactly the same volume of liquid- or solid-state particles enter the gaseous state as are converted back from the gas. At that point, the vapour reaches saturation level.

Although gaseous vapour is invisible, the term "vapour" is generally used to refer to a visible mixture of air and microscopic liquid droplets. The technical term for this is aerosol or liquid vapour.

VOCs (volatile organic compounds) are vapours e.g. from solvents such as paints, varnishes, adhesives or wood preservatives, in the workplace they can be particularly problematic.

Refers to a heterogeneous mixture in which microscopic liquid droplets are dispersed in gas. One example of this is water droplets in the air. The substances are so loosely mixed with one another that the individual components can be distinguished by the naked eye. Different areas of the mixture have different properties (such as colour, hardness and aggregate state) from adjacent areas.

Mist and aerosols become hazardous to health when the particles are inhaled deep into the lungs. Even disposable spray cans with flammable and highly flammable contents (e.g. corrosion protection spray, contact spray) can be problematic in the workplace.  Other examples are oil mists from cutting or grinding operations, and acid. The inhalation of such aerosols should be avoided.

Strictly speaking, a substance is a "gas" when a mass composed of this substance occurs in a gaseous aggregate state at a temperature of 20 °C and pressure of 1 bar (also known as the standard state). When this occurs, the molecules of the substance are entirely free to move, and the mass fills the available space completely and evenly.

Gaseous substances can be toxic or explosive. Even apparently harmless gases indirectly become life-threatening if they displace oxygen. In many cases it is recommended to do a clearance measurement of closed rooms in which gas is suspected before stepping in. Beside gas detectors, supplied air respirators and breathing apparatuses support workers within those conditions.