Warning Properties

By Tabitha Mishra
Last updated: October 15, 2022

What Does Warning Properties Mean?

The warning properties of chemicals or contaminants are the odor, taste, or irritating effects that alert people to their presence.

Warning properties are an important concept in respirator safety.

Safeopedia Explains Warning Properties

The Occupational Safety and Health Administration (OSHA) requires the use respirators in a variety of contexts, especially where workers my encounter oxygen deficient atmospheres, hazardous particulate matter, or airborne contaminants. Some respirators protect workers by filtering hazardous materials from the air, allowing them to breathe safely. Others seal off the atmosphere and supply the user with breathable air.

Regardless of the respirator type, when the user is able to detect the warning properties of a substance after donning the respirator, this is an indication that they are not protected from exposure to that substance.

Warning Properties and Permissible Exposure Limits

Warning properties are useful when they are easily detectable. A noxious smell or a tell-tale taste that is difficult to miss means that workers can rely on their senses to know whether their respiratory protection is compromised.

A hazardous substance has poor warning properties, however, if they are not easily detectable at concentrations greater than three times the substance's permissible exposure limit (PEL). In those cases, air-purifying respirators cannot be used, with two exceptions:

  • The air-purifying respirator has an end-of-life service indicators (ESLI) certified by the National Institute of Occupational Health and Safety (NIOSH)
  • Their use is permitted by a relevant OSHA standard

It is also important to remember that warning properties do not guarantee that every worker will be able to detect the presence of a harmful substance. Odor thresholds are median values for a population, which means that over half of the users will be unable to detect the odor until it exceeds the odor threshold.

Hazardous Substances Without Warning Properties

Unfortunately, some respiratory hazards do not have warning properties. Carbon monoxide, for instance, is colorless, odorless, and has no taste. This absence of warning properties is why it is known as "the silent killer."

When there is a risk of exposure to a substance with no warning properties, gas detectors or monitors are required to ensure that the atmosphere is safe.

Respirator Fit Testing and Warning Properties

Substances with notable warning properties are used in respirator fit tests. These tests ensure that the respirator creates a seal against the user's face and protects them from respirable hazards.

In the case of qualitative fit tests (QLFT), the user dons a respirator and one of the following substances is released into the air:

  • Isoamyl acetate, which smells like bananas
  • Saccharin, which has a sweet taste
  • Bitrex, which has a bitter taste
  • Irritant smoke, which causes coughing

If the user reacts to these substances or can detect their presence, this means the respirator is not fitted properly and will not provide suitable protection until this is corrected.


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