1/27/15 Update: This post is originally from 2013. We're sharing it again with the massive storm moving through Massachusetts. At least four people were killed in their automobiles during last weekend’s snowstorm, but the victims didn’t crash their cars after sliding on ice, nor did they plunge over an embankment. In fact, the cars weren’t moving at all—they were all parked. On Sunday morning, a 20-year-old man and 18-year-old woman were found dead in their snow covered, stationary car in Meriden, Conn. The same day, a 20-year-old man was found dead in a parked car in Mattapan, Mass. just hours after a teenage boy in Roxbury, Mass. died of the identical condition. Two other children in East Boston almost suffered the same fate, but were rushed to area hospitals and survived. In each case, someone had left the car running to provide heat, but didn’t realize the tailpipe was blocked up by snow. As a result, the vehicle cabin filled with odorless, invisible carbon monoxide, which poisoned the occupants.

The most insidious feature of carbon monoxide poisoning is that the early symptoms — mild nausea, dizziness, and weakness — are very mild and seem like mere car sickness.

Such tragedies don’t just happen in the winter. Back in the spring of 2008, 9-year-old Alejandro Thomasian and 11-year-old Jobanny Matias were in the rear seat of a Jeep Cherokee, enjoying a morning of four-wheeling with their dads in Lunenburg, Mass. When the vehicle got stuck in a muddy patch, the men got out to push and left the children in the warm cab. No one realized the exhaust pipe was blocked with mud until it was too late. Alejandro died of carbon monoxide poisoning, and Jobanny was hospitalized in critical condition and barely made it. That same month at the UMass Medical School, where I am a pediatric specialist, we treated a toddler who suddenly became limp and unresponsive while riding in her car’s back seat—she too had been poisoned with carbon monoxide from a malfunctioning, blocked tail pipe. After illegal and prescription drugs, carbon monoxide is the leading agent of accidental poisoning deaths, according to the Centers for Disease Control. And only a few decades ago, carbon monoxide was also commonly used for intentional suicide, as when people parked themselves in a closed garage and ran their cars. In 1975, the introduction of automotive catalytic converters—which turn most of the carbon monoxide into harmless carbon dioxide—dramatically cut the emitted amount of the poison. Suicide rates from the gas fell by half, and accidental poisonings fell by three-quarters. As one of our hospital’s emergency physicians recently emailed me, “You cannot imagine the number of people who put a hose from the tailpipe into the passenger compartment and find out several hours later that they ain’t dead.” Although this was a dramatic public health benefit, as the recent snowstorm cases dramatize, catalytic converters can’t remove carbon monoxide when the tailpipe is snow or mud-caked, since the blockage forces the gas to bypass the catalytic converter and escape. According to a 2007 report from the National Highway Traffic Safety Administration, 147 people still die each year from accidental carbon monoxide poisoning from cars. The most insidious feature of carbon monoxide poisoning is that the early symptoms — mild nausea, dizziness, and weakness — are very mild and seem like mere car sickness. Yet during this time, the poison enters the bloodstream, attacks red blood cells, and prevents them from carrying oxygen. The unsuspecting victim is being suffocated gradually from the inside.

Many cars tell you when it’s time for an oil change, if tire pressure is low, or when you’re low on gas. Why not also report if carbon monoxide levels are dangerous?