Paramedics assisted 2 sewermen suffering from cardiac arrest. As part of subcontractor cleaning crew, they were cleaning a laboratory’s hydraulic testing chamber using an acid solution. The 3-meter deep chamber contained sulphur water. One of the sewermen died. The second worker was seriously intoxicated while trying to rescue the first worker and dead shortly thereafter. A pronounced hydrogen smell was noted around the pit. A mobile chemical response unit took several samples on the day of the accident between 11.30 am and 4.30 pm. The H2S concentration in some of the samples was greater than 2,000 ppm. The workers were not wearing protective equipment and had not received sufficient training.