A Washington man's new car may have contributed to his mother's death in the oddest of ways. The News Tribune reports the 51-year-old Tacoma-area man woke at 4am Friday to get ready for work and discovered his wife hadn't returned from taking his 77-year-old mother home the night before.

He left to look for them and found the car parked several blocks away with the women unconscious inside. Also inside: four coolers of dry ice he kept in the back seat as part of his job as a Dippin' Dots ice cream delivery man.

Police believe some of the dry ice converted to gaseous carbon dioxide and escaped the coolers; that conversion happens as dry ice heats up. Police believe it reduced the amount of oxygen in the air and asphyxiated the man's mother, whom the Washington Post identifies as Hildegard Whiting; the man's wife, also 51, was in critical condition.

Det. Ed Troyer with the Pierce County Sheriff’s Department says the upgraded car may have been a contributing factor, as "the newer car probably had better sealing." He also noted it had been a hot day.

"This all happened due to a lot of circumstances lining up. Dry ice by itself isn't going to kill anybody," KOMO quotes him as saying.

"At this point we're just looking at this as horrific accident." The Post recounts other carbon dioxide-related deaths and incidents, including a scare the founder of Halo Top Creamery had in the company's early days when he was driving with dry ice and 40 pints of ice cream in his car.

(An unsecured boulder caused a deadly accident earlier this month in Minnesota.)

This article originally appeared on Newser: He Had Dry Ice in His Car for Work. It Likely Killed His Mom

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