A warning agent may also be called a clearing agent since it makes sure that the area is clear of people because they are forced to evacuate the site.
This is analogous to the warning agent added to natural gas, which gives a unique odor if there is a gas leak.
Reasons for using a warning agent:
(1) To let someone know that a fumigant is present at harmful levels.
(2) To force people without adequate protection to leave the area.
Qualities of a warning agent:
(1) The agent has some easily detectable quality.
(2) It can be detected at very low concentrations.
(3) It affects everyone.
(4) It can be mixed with the fumigant being used.
(5) It is not toxic in use.
A commonly used warning agent is chloropicrin. This is a fumigant that has a strong odor and which is irritating to people at a low concentration.
