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The clumping of powder particles bound together into clusters containing trapped air.

Air Classification
Air classification is a technique by which dry powders of mixed particle size are separated into two distinct fractions, one above and one below a definite cut point. This is achieved by exploiting the differential forces acting upon particles of different size and mass within an air flow system. Different techniques can be required to achieve this depending on the material and particle sizes involved and British Rema has a full range of classifier options available to meet a wide range of operating parameters.

Attrition refers to wearing down or grinding by friction.

Bulk Density
Mass per unit of volume: in powder form this includes the air trapped between the particles.

Control of Substances Hazardous to Health Regulations 2002
Regulations requiring employers to control exposure to hazardous substances to prevent ill health to employees and others (see www.hse.gov.uk/coshh).

A term that describes powder in a state of suspension using compressed air, creating a fluid mixture of air and powder.

Fluidised Bed
A container in which powder is suspended in a continuous stream of air.

Friability refers to the ease with which a solid material can be crumbled or reduced to powder by attrition.The friability depends on the nature of the applied forces as well as the intrinsic physical properties of the material itself. There is, consequently, no absolute measure of friability but a variety of methodologies designed to provide relative measurements when applied to a specific application.

Grinding, milling and micronisation
All three terms refer to the reduction of particle size by mechanical methods and are somewhat interchangeable. Although there is no fixed rule, typically, the term micronisation is used where the resulting particle size is required to be less than 10 microns and for many applications an “air-microniser” (spiral flow jet mill or opposed jet mill) would be required to achieve these particle sizes. Refer to our Equipment Selection Guide for further details.

HSC - Health and Safety Commission
(Merged with HSE on 1 April 2008)

HSE - Health and Safety Executive
A public body in the United Kingdom responsible for the encouragement, regulation and enforcement of workplace health, safety and welfare, and for research into occupational risks.

ISO 9001
A quality management system standard, defined and maintained by the International Organisation for Standardisation (see www.iso.org) and administered by national or international accreditation and certification bodies. Requirements include:

  • a set of procedures that cover all key processes in the business
  • monitoring processes to ensure that they are effective
  • the keeping of adequate records
  • the checking of output for defects, with appropriate and corrective action
  • the regular review of individual processes and the quality system itself for effectiveness
  • facilitating continuous improvement

A company or organisation that has been independently audited and certified to be in conformance with ISO 9001 may publicly state that it is "ISO 9001 certified" or "ISO 9001 registered". Certification to an ISO 9000 standard does not guarantee any quality of end products and services; rather, it certifies that formalised business processes are being applied.

LEV (local exhaust ventilation)
Air extraction system designed to remove airborne contaminants.

"Mesh size" covers a number of alternative scales used for the definition of particle size, all based on identifying the smallest of a series of meshes, or sieves, of reducing grid size through which a particle will pass. The numerical value in any particular scale generally refers to the number of openings per unit of length or area and, hence, the higher the number the smaller the particle size. There are a number of different scales in use and three of the most common (US mesh, Tyler screen and BSS mesh) are set out in the Particle Size Comparison Chart with the equivalent particle sizes expressed in microns.

Micron is a commonly used alternative term for micrometer. It is one millionth of a meter (1×10−6 m) and the usual notation is "µm" (using the Greek letter mu).

Mohs scale of mineral hardness
Hardness measures a mineral's resistance to scratching and reflects its atomic structure. The Mohs' scale is commonly used to describe the hardness of materials and compares a material’s resistance to scratching against a standard set of reference minerals from talc (Mohs hardness 1) to diamond (Mohs hardness 10). The hardness of a material is measured against the scale by finding the hardest material that the given material can scratch, and/or the softest material that can scratch the given material. The scale is not linear and the table below shows comparison with absolute hardness measured by a sclerometer.

Mohs' scale of mineral hardness

 Mohs No.Hardness

 Standard Mineral

Absolute Hardness

















 Orthoclase Feldspar















PPE - personal protective equipment
e.g. face masks, respirators, protective clothing

PSD - (particle size distribution)

Safe System of Work
A formal procedure that results from the systematic examination of a task in order to identify all the hazards. It defines safe methods of working to ensure that hazards are properly controlled.

Terminology and size
There are a number of terms commonly used to describe particle size.Whilst there are no fixed definitions, the following table can be used as a guide:


 Particle Size



 <100 mm


 Medium Coarse

 10 mm


 Medium Fine

 1 mm

 1000 microns


 0.1 mm

 100 microns

 Super Fine

 0.025 mm

 25 microns

 Ultra Fine (Micronised)

 0.010 mm

 10 microns


 0.005 mm

 5 microns


WEL (workplace exposure limit)
The maximum concentration of an airborne susbstance, averaged over a reference period, to which employees may be exposed by inhalation. WELs are set by the HSE and listed in EH40/2005.