A farmer and 16 of his cattle have died in a freak accident after a “deadly dome of air” formed in a Wisconsin farm’s manure holding tank.

According to WAOW, a 29-year-old farmer named Michael Biadasz, from Amherst, Wisconsin, died of gas poisoning on his family’s farm after being overcome by fumes of either methane or sulfur oxide. Initially, 13 of the farm’s cattle died as well; later, three more expired, bringing the total to 16 cattle deaths.

Biadasz was reportedly found dead when other workers arrived to begin hauling manure away from the tank.

Rifleman told WSAW that gas poisoning deaths typically occur in closed areas, making the incident even more surprising. The coroner said that atmospheric pressure prevented the gases from dissipating.

The coroner went on to say that an investigation is underway to determine exactly what caused Biadasz’s death. According to Rifleman, Biadasz had safely emptied the same tank hundreds of times prior to the fatal incident.

“As if there isn’t already enough danger in the lives of farmers, this family had to suffer this freak accident,” one Facebook user commented on the story. “So sad.”

Following the tragic accident, many are calling for tougher regulations to be placed on manure holding tanks to prevent a similar incident in the future. According to All That’s News, the National Agriculture Safety Database says that there should be proper ventilation in areas where animals are stored and that warning signs must be posted nearby.

WASW reports that a similar unfortunate fate befell a Virginia family in 2007, when five of its members died as a result of a pipe blockage that caused a fatal buildup of methane gas.