Hundreds of workers of a Japanese-invested company in the northern Vietnamese province of Quang Ninh went on strike on Tuesday, demanding an explanation to the ‘mysterious gas’ that had previously caused many of them to faint.

Employees of Yazaki Co, situated within the Dong Mai Industrial Park, demanded that they know the reason behind the incident before going back to work.

Dozens of the firm’s workers were disoriented and lost consciousness shortly after beginning their work on Friday last week.

They were promptly admitted to the hospital for emergency treatment.

After evaluating the victims’ health conditions, the provincial Department of Health believed that they had suffered from heat stroke.

Meanwhile, Yazaki said workers might have been affected by pesticide sprayed by local residents on nearby crops at the time of incident.

The workers refuted both explanations, asserting that they had inhaled some kind of strange gas coming from the firm’s warehouse.

It was only around 8:00 am at that time, meaning workers were not likely to be affected by heat stroke, especially when workshop had a sufficient system of ventilation and air conditioners, according to the employees.

Hundreds of workers refuse to work on July 10, 2018. Photo: Tuoi Tre

The Quang Ninh People’s Committee has recently requested Yazaki to ensure a safe working environment for its employees and tasked the health department, in coordination with local experts, with assessing the case.

Initial evaluation of specialists showed that the amount of formaldehyde at two out of five locations of the company exceeded the normal limit on the day of the incident, news website VnExpress quoted Nguyen Tien Hung, deputy director of the provincial health department, as saying on Tuesday.

The formaldehyde levels were back to normal rates the following days.

Excessive amount of formaldehyde can cause nausea, dizziness, difficulty breathing, and skin irritation, Hung stated.

However, it is not certain whether or not the chemical compound was the cause of the situation at Yazaki, as test results of the victims did not show the presence of formaldehyde, he added.

The workers are treated at the hospital on July 6. Photo: Tuoi Tre

Experts from the Hanoi-based Bach Mai Hospital will conduct further tests to find out the exact cause, the health official said.

Specializing in the production of automotive parts, Yazaki Company in Quang Ninh Province has the capital investment of US$35 million and is employing nearly 3,000 people.