Last updated on 23 October 2026
Short answer: a ship is declared gas-free after fumigation when a competent person has ventilated the holds and cargo, measured the gas concentration and issued a gas-free certificate. Only then is the fumigation complete under the IMO recommendations and can discharge begin. EWS Group, a fumigation and gas measurement specialist, measures and certifies ships gas-free in European ports and at sea.
What is in-transit fumigation?
In-transit fumigation is the fumigation of cargo in a ship’s holds during the voyage. It is a common treatment in the international trade in grain and other bulk cargoes, such as wood pellets, logs and seeds. It kills insects, their eggs and larvae in the cargo and prevents pests spreading via the cargo. Millions of tonnes of cargo are fumigated at sea every year. The most widely used fumigant is phosphine, released from tablets or pellets.
Why must a ship be declared gas-free after fumigation?
Fumigants are highly toxic to humans, and fatal accidents have occurred when people entered holds or discharged fumigated cargo. Under the IMO recommendations on the safe use of pesticides in ships, fumigation is not complete until the holds and cargo have been ventilated and tested and a competent person has certified that they are free from harmful concentrations of gas. Only then can discharge begin safely.
How is a ship declared gas-free?
Declaring a ship gas-free involves four steps:
- Notification: before arrival, the master, owner or agent informs the port or terminal that the cargo has been fumigated.
- Ventilation: the holds and cargo are ventilated so the fumigant can escape.
- Measurement: a competent person wearing respiratory protection measures the gas concentration in the holds and cargo; the readings are recorded in the ship’s logbook.
- Gas-free certificate: if the concentrations are safe, the competent person issues a gas-free certificate and the warning signs are removed.
Fumigant tablet residues are removed from the holds immediately on arrival at the discharge port.
Why is a gas-free certificate not a guarantee for the whole discharge?
A gas-free certificate reflects the situation at the time of measurement. During discharge, moving the cargo can release pockets of fumigant trapped deep in the stow, and on short voyages fumigant tablets may not have fully decomposed. Measuring during discharge therefore remains important, and anyone working in or near the holds should carry a personal gas detector.
Who is responsible during fumigation on board?
During fumigation on board, responsibilities lie with different parties:
- Fumigator-in-charge: responsible for the fumigation itself and, where appropriate, for removing fumigant residues.
- Master: responsible for safe working conditions on board during the voyage; at least two crew members, including one officer, must be trained in handling fumigants.
- Competent person at the discharge port: measures the gas concentration and issues the gas-free certificate.
What happens to fumigant tablet residues?
After discharge, the residues of the phosphide tablets, in the form of sleeves or plates, remain in the holds. Tablets that have not fully decomposed during the voyage can still release phosphine when they come into contact with moisture. Phosphine residues are classed as hazardous waste suitable only for incineration, so they must be collected, transported and disposed of safely.
How does EWS Group help with gas-free certification and degassing of ships?
EWS Fumigation, part of EWS Group, measures fumigated ships and certifies them gas-free, in port and at sea, throughout Europe:
- Gas measurements on board: experienced fumigation specialists measure the gas concentration in the holds and cargo.
- Gas-free certificate: after measuring, EWS Fumigation issues a gas-free certificate so discharge can begin.
- Residue removal and ventilation: in several European ports, EWS Fumigation removes fumigant residues, after which the ship can continue to its final destination, properly ventilated.
- Disposal: EWS Group transports and processes the waste and provides the S-form (for ships), waste transfer note or CMR that officially takes the waste off the customer’s hands.
For phosphine waste, EWS Group holds a VIHB registration as a waste collector, and ADR certificate for transporting dangerous goods, an environmental permit to store and neutralise the waste, and permits from the Rotterdam and Amsterdam port authorities to collect phoshine residues from seagoing vessels.
See the Fumigation and Gas Measurement service pages.
Frequently asked questions about gas-free certification of ships
When can a fumigated ship be discharged? Only once a competent person has measured the holds and cargo and issued a gas-free certificate.
Who collects fumigant tablet residues? A licensed waste collector with the right permits. EWS Group holds a VIHB registration, an ADR certificate and permits from the Rotterdam and Amsterdam port authorities to collect phosphine residues from seagoing vessels.
Which fumigant is most commonly used on ships? Phosphine, released from aluminium phosphide tablets or pellets. Phosphine is highly toxic and also flammable.
Who can declare a ship gas-free? A competent person, for example from a fumigation company, with the right measuring equipment and respiratory protection.
Is a ship declared gas-free completely safe? A gas-free certificate reflects the situation at the time of measurement. Pockets of gas can still be released from the cargo during discharge, so gas detection and caution remain necessary.
Must the port be told that the cargo has been fumigated? Yes. Before arrival, the master, owner or agent informs the port or terminal that the cargo has been fumigated, even if it has already been ventilated during the voyage.
Source: Maritime and Coastguard Agency (UK), MGN 700: Guidance on the safe use of pesticides in ships (May 2024), summarising IMO recommendations MSC.1/Circ.1264.
