Dry ice, the frozen form of carbon dioxide, is wonderfully helpful in a variety of industrial and scientific applications thanks to its ability to rapidly chill anything it touches and because, rather than melting, it changes into gas once exposed to natural ambient temperatures and atmospheric pressures. The latter process, called sublimation, is also very cool to look at, which helps explain mankind’s fascination with the substance.

Yet as a tragic story out of Washington state reminds us, quickly accumulating plumes of CO₂ gas can be incredibly dangerous. According to the Pierce County Sheriff’s Department, a 77-year-old woman has died and her 51-year-old daughter-in-law is in critical condition after the two drove around in a car containing improperly stored dry ice.

Investigators reported that the unidentified survivor was driving the now-deceased woman home on Thursday night in a car belonging to her husband, an ice cream salesman. He had previously placed four coolers of dry ice in the vehicle, intending to use it to keep an upcoming order frozen.

After waking at 4 am on Friday to find his wife still gone, the man ventured outside and found his car parked several blocks away, his wife and mother unconscious inside. He apparently broke the window open with a rock and called 911. After an ambulance arrived, his mother was pronounced dead at the scene and his wife was taken to the hospital.

The local medical examiner later ruled that the older woman died from suffocation, likely because the dry ice rapidly converted into gas and displaced the oxygen within the car.

“Somehow or another, the fumes escaped from the coolers,” Detective Ed Troyer told KOMO News. “Possibly because it was so hot outside and because he had a newer car. It probably had better sealing and less ventilation.”

“It was a combination of things that went terribly wrong,” Troyer continued. “Dry ice by itself isn’t going to kill anybody.”

Beginning almost immediately after higher-than-normal concentrations of CO₂ are inhaled, the body’s autonomic nervous system is triggered (by lowering cerebrospinal fluid pH) to reset the balance by breathing faster and deeper. If CO₂ continues to build up in the bloodstream, one will lose consciousness quite rapidly.

Containers of dry ice typically bear warnings about inhaling the vapor and keeping it stored in well-ventilated areas.