Chlorine gas is primarily a respiratory irritant. At low concentrations, chlorine gas has an odor similar to household bleach. As the concentrations increase from the level of detection by smell, so do the symptoms in the exposed individual. Depending on the level of exposure to chlorine, the effects may become more severe for several days after the incident. Observations of exposed individuals should be considered part of the medical response program.
The following list is a compilation of potential chlorine exposure thresholds and potential responses in humans, with considerable variation among subjects:
| Table 1 | Chlorine Exposure Thresholds in ppm and Reported Responses |
| 0.2 - 0.4 | Odor threshold (decrease in odor perception occurs over time) |
| 1 - 3 | Mild mucous membrane irritation, tolerated up to 1 hour |
| 5 - 15 |
Moderate irritation of the respiratory tract. |
| 30 | Immediate chest pain, vomiting, dyspnea, cough |
| 40 - 60 | Toxic pneumonitis and pulmonary edema |
| 430 | Lethal over 30 minutes |
| 1000 | Fatal within a few minutes |
Excerpt from Chlorine Basics LINK, Section 7.1
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