There are hazards that come with using phosphine fumigants, which are widely used on farms to control pests.
Phosphine fumigants are widely used on farms to control insect, rodent and rabbit infestation in many different stored grains. However, there are various hazards associated with their use.
Metal phosphide tablets release toxic phosphine gas when they contact moisture (either in air or fluids). These chemicals are effective, cheap and easily applied. However, consideration must be given to the associated hazards from inhalation of toxic gas and explosion.
When phosphine gas is inhaled, it can react with moisture in the lungs to form phosphoric acid, which can be serious or fatal. Other symptoms of poisoning from inhalation are:
- coughing, chest tightness and headache
- double vision and dizziness
- nausea and vomiting.
Exposure may also lead to anaemia, bronchitis, diarrhoea and visual, speech and motor disturbances.
If a person has been overcome by phosphine gas, the rescuer must wear adequate breathing protection to avoid also becoming a victim.
Phosphine gas has an odour of decaying fish. However, do not rely on the odour of phosphine to determine whether the atmosphere is safe, because the odour threshold for phosphine is above the exposure standard. If the odour threshold for phosphine is detected, evacuate the area immediately.
Inhalation of the gas may occur from:
- leakage from fumigated silos or stacks
- inappropriate fumigation practices, including in enclosed sheds
- sleeping in trucks which have had phosphine placed in the load
- entering or examining silos or stacks immediately after fumigation
- leaving tablets and/or canisters in inappropriate places (e.g. floor of utility)
- cleaning and/or hosing out silos that have been used for fumigation when the product has not reacted completely.
- Phosphine gas is flammable and may ignite when concentration in the air exceeds 1.8%.
- Flammability risk is greater when humidity is high, which may cause gas to be emitted quickly upon opening the canister.
- Extinguish all potential ignition sources before opening. Open the container slowly, with the top pointing downwind and away from the face or body.
- Materials added to tablets release carbon dioxide and ammonia with phosphine gas, which are designed to prevent spontaneous ignition of the gas under normal circumstances.
- Store canisters correctly to prevent deterioration of the tablets, thereby reducing explosion potential. Keep them in a cool, dry place away from all habitation.
- Phosphine gas also reacts violently with acids and with compounds containing fluorine, chlorine, bromine and iodine.
- Do not place tablets into tarped truck loads of grain.
Other safety practices
Always read the label before use and follow the manufacturer's instructions.
- Obtain a safety data sheet (SDS) from your chemical supplier which gives information about treatment and symptoms of phosphine poisoning, as well as chemical data.
- Wear correct respirator and protective clothing (see SDS and label). Impervious gloves (e.g. PVC) should be worn when dispensing pellets by hand.
- Have an observer standing by who should have access to respiratory protection.
- Clearly sign all areas under fumigation as directed by the Pest Management Regulation.
- Inform workers that an area is under fumigation.
- Never use phosphine while grain is in transit.
- Monitor the atmosphere around fumigation using a hand pump and gas detector tube; concentration should not be higher than 0.3 ppm.
- Before moving grain after fumigation, ensure that all gas fumes have been dispersed. It is inadvisable to treat grain in airtight containers because of difficulties dispersing all gas fumes.
- Open phosphine containers in the open air, not in the shed or silo.
- Store containers appropriately.
- Dispose of spent phosphine tablets correctly.
- Never dispose of surplus or part-filled containers in tips or other rubbish by burial. Others, especially children, could locate the container and be exposed to injury risk.
- Never increase dosage to have a 'better kill' of insects.
- Always keep out of reach of children.
- A full-face filter respirator or self-contained breathing apparatus must be worn if concentrations exceed 0.3 ppm.
- The filter must be approved for phosphine and suitable for short-term exposure only (type B for inorganic gases).
- The filter should be immediately discarded and destroyed if there is any hint of phosphine odour inside the face-piece.
- Self-contained breathing apparatus should be used for operations, such as breakdowns, when longer exposures at higher concentrations may occur.
- Facial hair will prevent an adequate seal of the mask against the skin.
- A suggested life of one hour for filters, at usual exposure levels of operators in routine testing procedures, is a recommended safeguard.