Week 38: Flammables (Combustible Dust)

Flammables — Combustible Dust

Combustible dust is defined as a solid material composed of distinct particles which present a fire hazard when suspended in air. A dust explosion can cause catastrophic loss of life, injuries, and destruction of property.

combustible dust

Characteristics of a dust explosion

  • Definition: A dust explosion can be defined as a rapid release of high pressure gas into the environment.
  • Process:
  1. It commonly begins with the ignition of a fuel, such as a combustible dust, that burns very rapidly.
  2. It produces a large and sudden release of gas and does not necessarily involve a fire.
  3. There are often more serious secondary explosions that result from an initiating explosion
    which dislodges loose particulates.
  • Five criteria that must be present for dust explosion conditions:
  1. Fuel, i.e., combustible dust
  2. Heat or an ignition source
  3. Oxygen, which may be in the form of an oxidizer chemical
  4. Dispersion of dust particles of a certain concentration and quantity
  5. A confined dust cloud

Examples of industries where combustible dusts are common:

  • Grain handling
  • Flour production
  • Industries using wood
  • Sugar manufacturing
  • Certain types of plastic
  • Coal handling
  • Textile industries using cotton, nylon, etc.
  • Metal production such as aluminum, sodium, and potassium

Fighting dust accumulation:

Assure that dust-containing systems, ducts, and dust collectors are designed in a manner that prevents fugitive dusts from accumulating in the work area. This includes proper air velocity and enough volume in the dust collectors for the various applications.

  • Assure that the working surfaces are designed in a manner to minimize dust accumulation and to facilitate cleaning.
  • Accumulations on overhead beams, joists, ducts, the tops of equipment, and other surfaces must be included when assessing dust concentrations.
  • Your facility must have a housekeeping program with regular cleaning frequencies established for floors and horizontal surfaces, including ducts, pipes, hoods, ledges, and beams, to minimize dust accumulation within operating areas of the facility.
  • Housekeeping practices must include immediate cleaning whenever a dust layer of 1/32-inch thickness accumulates over a surface area of 5% or more of the floor area of the facility or any given room.
  1. If the floor area exceeds 20,000 ft2, a dust layer must not exceed a 1,000 ft2 floor area.

Controlling heat and ignition sources:

  • Electrical equipment must meet Class II requirements for explosion proof control. This includes electrically-powered cleaning devices such as vacuum cleaners.
  • An effective ignition control program must be in place.
  • Include in the program such elements as grounding and bonding, metal detection, preventive maintenance programs, and other methods.
  • An effective program will dissipate any sparks or electrostatic charge that could be generated where a combustible atmosphere may exist (e.g., in ductwork).
  • Implement a hot work permit program.
  • Post and enforce no smoking areas.
  • Assure that duct systems, dust collectors, and dust-producing machinery are bonded and grounded to minimize accumulation of static electrical charge and equipped with spark detection and arrest systems.
  • Use industrial trucks, machinery, and electrical equipment that are approved for Class II combustible dust locations.

Follow these control measures to avoid dust build-up and prevent dust explosions.