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When is the best time to provide protection from hazards?

When hazards are identified, it is useful to consider general principles of control, which can be thought of as two basic categories: "pre-contact" or "point-of-contact."


Pre-contact control is the first and most important method because it prevents the hazard from reaching the worker. Pre-contact control methods include substituting materials or processes that are less hazardous, isolating hazardous processes, retrofitting existing equipment, or acquiring safer equipment. Pre-contact control can also be achieved by providing protection to the worker with local exhaust ventilation, machine guarding, better housekeeping, and safe work practices. Many Canadian jurisdictions legislate pre-contact controls. While many hazards can be anticipated and avoided through effective engineering at the pre-contact stage, others may not be recognized before an accident occurs. A thorough effort to identify hazards is essential so that hazards may be reduced or eliminated at the source.

Where pre-contact controls are not practical, feasible, or totally effective then point-of-contact controls must be used.


The point-of-contact control is important but secondary because it cannot eliminate the hazard. It only manages the hazard at the point of contact with the worker. This form of control is primarily accomplished through personal protective equipment. It is to be used when pre-contact controls are not totally effective.

Choosing a Respirator

When should a respirator be used?

Workers should use respirators for protection from contaminants in the air only if other hazard control methods are not practical or possible under the circumstances. Respirators should not be the first choice for respiratory protection in workplaces. They should only be used:

  • when following the "hierarchy of control" is not possible (elimination, substitution, engineering or administrative controls)
  • while engineering controls are being installed or repaired
  • when emergencies or other temporary situations arise (e.g., maintenance operations)

How should you control respiratory hazards?

Respiratory hazards can include airborne contaminants such as biological contaminants, dusts, mists, fumes, and gases, or oxygen-deficient atmospheres. Note that more than one respiratory hazard can be present at the same time. After elimination and substitution, well designed and maintained engineering controls are the preferred methods of controlling worker exposure to hazardous contaminants in the air. These control methods include:

  • mechanical ventilation
  • enclosure or isolation of the process or work equipment
  • proper control and use of process equipment, and
  • process modifications including substitution of less hazardous materials where possible.

Administrative controls may be used in addition to engineering controls. Administrative controls limit workers' exposures by scheduling reduced work times in contaminant areas or by implementing other such work rules. These control measures have many limitations because the hazard is not removed. Administrative controls are not generally favoured because they can be difficult to implement, maintain and are not reliable.

What are IDLH considerations

Some types of atmospheres contain concentrations of hazardous substances that places the worker in immediate danger because these concentrations would impair the ability to leave the work area (self rescue) or potentially cause irreversible health effects, including serious injury or death in a matter of minutes.

There are particular conditions that are considered "Immediately Dangerous to Life or Health (IDLH)". These include:

  • A known contaminant at a concentration known to be IDLH
  • A known contaminant at an unknown concentration with the potential to be IDLH
  • An unknown contaminant at an unknown concentration
  • An untested confined space
  • An oxygen-deficient atmosphere
  • Firefighting
  • Contaminants at or above 20% of their lower explosive limit (LEL—the concentration at which the gas or vapour could ignite)