In late December subcontractor Transocean - which operates the Development Driller 1 rig on the Gorgon field offshore north Western Australia - was issued a prohibition notice and occupational health and safety improvement notice from the offshore oil and gas regulator.
The notices were made public today and issued to Transocean subsidiary Sedco Forex.
According to the National Offshore Petroleum Safety and Environmental Management Authority (NOPSEMA), which issued the notices, a planned inspection of the rig found "airborne hazardous chemical dust" which was not being controlled during a chemical mixing operation.
Transocean and Chevron immediately implemented what is known as a ‘work around' requiring workers conducting chemical mixing to wear respirators.
However, a further inspection found that the respirators were "unsuitable", and the operator had not met its policies by providing higher-grade Atmosphere Supplying Respirators.
The regulator also noted that there was no respirator filter change schedule in place.
"No evidence was produced to demonstrate that the facility operator had taken measures to determine the level of airborne contaminants," NOPSEMA said.
"Therefore, members of the workforce involved in mixing hazardous chemicals at the manual hopper are being exposed to an unknown concentration of airborne hazardous chemical dust during mixing chemicals at the manual hopper."
The rig has a ventilation system in the mixing room, however it was deemed "ineffective at capturing the chemical dust" and was in fact venting it back into the work area contaminating the air workers were breathing.
NOPSEMA warned workers could be exposed to "serious" health effects including permanent, progressive or irreversible skin and eye damage.
Workers were at risk of permanent disabling or a major reduction in quality of life, according to the regulator.
Energy News understands the rig was not shut-in and production from the field was not affected.
Transocean has been ordered to partially enclose the mixing table where the chemicals are combined and ensure air from the room is discharged safely.
The company has also been ordered to introduce an exposure assessment of workers to demonstrate airborne toxins and chemicals are contained and controlled or find another way to reduce the risk "to a level that is as low as practicable."
Chevron and Transocean were both approached for comment.
