There are hazardous gases that workers encounter commonly in industry that are discussed more often than others. For example, information about gases like carbon monoxide and hydrogen sulfide is readily available—where they come from, what immediate danger they present, and what long term health effects they pose. But there are other hazardous gases that may be present in your worksite that many people are considerably less aware of. One of these gases is phosphine. So what do you need to know about phosphine gas?
Phosphine is a highly toxic, flammable gas identified by the chemical formula PH3. It is heavier than air and is prone to collecting in low lying areas. It can be self-igniting, and may ignite in air at any concentration above 1.79%. Phosphine is colorless, and in its pure form, odorless. However, it has a strong odor of garlic or rotting fish when it is encountered in an otherwise normal atmosphere.
Phosphine gas is used as a dopant in the semiconductor industry. It is added as an intentional impurity to produce certain characteristics in semiconductors. However, it is more widely known for its role as a fumigant in the agriculture industry. Phosphine is a pesticide that kills insects and rodents during the storage and transportation of grains.
It is typically introduced to the grains in the form of aluminum phosphide, calcium phosphide or zinc phosphide pellets that are placed on top of silos, grain bins, cargo holds or rail cars. The pellets release phosphine gas as they react with moisture in the atmosphere or in the grain itself. In these applications, concentrations of phosphine may exceed 200 parts per million (PPM). Sometimes phosphine gas is introduced directly to the grains, but in those cases, it is diluted with carbon dioxide or nitrogen to reduce its flammability and the danger of explosion.
The OSHA Permissible Exposure Limit (PEL) for phosphine and the NIOSH Recommended Exposure Limit (REL) are both set at a total weight average (TWA) of 0.3 PPM. The NIOSH Short Term Exposure Limit is set at 1 PPM. Phosphine is immediately dangerous to life and health at a concentration of 50 PPM. Exposure to phosphine at this concentration for longer than 30 minutes may cause death. Phosphine can be absorbed into the body by inhalation where it then attacks the respiratory tract. Exposure to phosphine gas above the recommended limits may cause:
Because of the wide range of hazards that phosphine presents, there are several methods of detecting the gas. Most portable gas detectors with phosphine detection capability use electrochemical phosphine sensors. These sensors have a maximum detection range of 10 PPM or less and are ideally suited to monitoring personal exposures to the gas.
However, in many agricultural applications, phosphine may be present in higher concentrations. For this industry, sensors may be found with a measuring range of up to 500 PPM that sacrifice precision at lower concentrations. A PID sensor with a standard 10.6eV lamp can also be used to detect phosphine as a toxic hazard. To protect against explosion from phosphine, a standard catalytic bead oxygen sensor may be used.
You must always be aware of the hazards that you may encounter in your work environment and protect yourself against them. If you work in the semiconductor or grain industries, be sure to protect yourself from the dangers of phosphine by increasing your awareness and choosing the right detection method.
Learn more about how to detect phosphine, including the best gas detectors for the job.
Dave Wagner is director of product knowledge and application engineering at Industrial Scientific.