An unnamed Washington man lost his mother on Friday after a dry ice cooler suffocated her inside his delivery vehicle.

The Pierce County Medical Examiner’s Office ruled the death as “asphyxiation due to displacement of oxygen by carbon dioxide,” according to a report by The News Tribune. What should have been a simple delivery of the popular “Dippin’ Dots” summer treat resulted in the hospitalization of the man’s wife, and the death of his 77-year-old mother.

The University Place resident first called for medical assistance when he found his wife and mother passed out in his car in the wee hours of Friday morning. His mother had been visiting him, and his wife had agreed to drive her home. When he got up for work at 4:00 AM, he realized she had not returned.

After finding them, the man then broke the locked car’s window with a rock and called 911. Unfortunately, he was too late to save them both. While his wife was immediately transported to Tacoma’s St. Joseph Medical Center in critical condition, his mother was pronounced dead at the scene.

Dry ice, a super-cold solid form of carbon dioxide, turns back into a gas as it thaws. The phenomenon is often used in in stage “smoke” machines for dramatic effect, but can be deadly in confined spaces. While the problem may have existed before, the family had “recently got a new car,” according to sheriff’s spokesman Ed Troyer. “The newer car probably had better sealing.”

No foul play is suspected. “At this point we’re just looking at this as horrific accident,” Troyer said. Personally, Troyer could not recall another instance of dry ice asphyxiation in his career, but “if you do some research on it, it’s out there, it happens.”