Rolex employees fled after an incident prompted the evacuation of one its manufactures at noon on Wednesday.

According to local reports, the Rolex manufacture in Chêne-Bourg, near Geneva, was evacuated after a runaway chemical reaction following the mixing of certain products released toxic fumes in one of its workshops. The intervention is still ongoing but the reaction has been contained, the Fire and Rescue Service said.

It’s unclear what chemicals were mixed, but the site is responsible for the production of dials, including gem-setting, as well as the production of Cerachrom bezels.

Recent patents filed by Rolex have revealed the challenges the manufacture faced of producing certain color combinations for its ceramic bezels, as zirconia must be mixed with other chemical compounds, primarily mineral pigments.

Four trucks, 20 firefighters and one ambulance were dispatched to the scene, according to the Fire and Rescue Service. No injuries were reported.