Gorgon leading partner Chevron has conducted medical checks on hundreds of workers after possibly exposing workers during a bungled clearing of asbestos on Barrow Island.

Samples taken from where workers were loading and unloading containers have proved positive to the deadly blue and white asbestos fibres.

"Workers were transporting drums containing asbestos. Some of these drums were not marked or sealed properly, nor were workers told what their cargo contained. It seems that asbestos has spilled onto the pallets and the dirt surrounding the work area," said a furious Chris Cain, Secretary of the Maritime Union of Australia.

"There are a laws, regulations and codes of practice as long as your arm about how to handle this lethal material. Chevron itself has its own so-called ‘Operational Excellence Management System", but as far as I can see all of this was ignored and these workers are likely to have been exposed to some of the most dangerous fibres known," Chris Cain said.

Unions raised the alarm after laboratory testing of samples around the loading work area came back positive to asbestos. "Unions raised this issue with Chevron over a week ago, but so far there has been no response," UnionsWA Secretary Simone McGurk said.

Unions are also critical of the response by WorkSafe, who took over a week to attend the site.

Further testing around loading and supply base facilities in Dampier have also come back positive to containing asbestos, increasing the likelihood of a number of maritime and transport workers who may have been exposed.

"The biggest concern is for workers who may have been exposed to fibres," Simone McGurk said. "But if we are correct, and there has been such an obvious breach of procedures in the removal of asbestos containing material, then we will do all that we can to make sure that it doesn't happen again and the employers involved are brought to book."