The 36 people who died in a warehouse fire in California probably died of smoke inhalation, authorities have said. According to a report from CBS, the intense flames of the blaze in Oakland produced “thick billowing black smoke” and the victims died before any fire or structural collapse around them.

“Meanwhile, the Bureau of Alcohol, Tobacco, Firearms and Explosives said Tuesday afternoon that it is looking at the possibility that a refrigerator or other appliance was the source” of the fire last week at the warehouse, which had been housing artistic space and, when the flames broke out, a dance party.

Most people caught in fires typically die of smoke inhalation as opposed to actual burns. The National Fire Protection Association explains that smoke inhalation hits fast: “Smoke incapacitates so quickly that people are overcome and can’t make it to an otherwise accessible exit.” Fire eats up all the available oxygen, leaving people with little to breathe. When oxygen levels dip below the normal 21 percent found in outdoor air, people lose their judgment and coordination, then suffer a headache, dizziness, nausea and fatigue. At 9 percent oxygen, a person falls unconscious and at 6 percent they experience respiratory or cardiac arrest.

Read: Burn Victim Takes Off Mask

Aside from fire affecting oxygen levels, the heat of the air can burn the respiratory tract — “when the air is hot enough, one breath can kill” — and there are tiny particles that lodge in the lungs and impair the respiratory system. Part of what makes it so deadly is the fumes, the NFPA says. After the fire consumes most of the oxygen in the room, it slowly burns material in the home and, through that process, releases toxic gases. “The most common, carbon monoxide (CO), can be deadly even in small quantities, as it replaced oxygen in the bloodstream.” There could also be hydrogen cyanide, which interferes with the functioning of your cells, and phosgene, which can irritate the eyes and throat and force fluid to build up in the lungs.

Carbon monoxide is usually recognized as a lethal gas in scenarios other than fires — it is colorless and odorless and kills, for example, people in confined or otherwise unventilated spaces where it is being produced, such as from the exhaust pipe of a car or a hot water heater. The Centers for Disease Control and Prevention say carbon monoxide poisoning, which reduces the body’s supply of oxygen, comes with a headache, dizziness, weakness, vomiting, chest pain and confusion. “If you breathe in a lot of CO it can make you pass out or kill you.”

When it comes to smoke inhalation in general, Michigan State University lists symptoms as coughing, vomiting, sleepiness and confusion. “If you notice a fire victim has difficulty breathing, singed nostril hair, and burns to their nose, mouth or face, seek immediate medical attention for them. … Over 50 percent of people with severe burns and smoke inhalation die.”

See also:

Teens Deliberately Setting Themselves On Fire

Teen Who Died Of Cancer Is Cryogenically Frozen