Thirteen people were sent to hospital after with carbon-monoxide poisoning as a result of a leak in an office building in the 1600 block of West 5th Avenue.
Two people were in critical condition.
Paramedics who arrived on the scene became aware of the cause of the problem when their carbon-monoxide monitors went off.
Over Twitter, paramedic Jodi Butterman explained that they've been wearing these devices since 2017.
"They're critically important," she said. "They save lives. It is very important that people put them in their houses, in their buildings—their office buildings."
The monitors provide a reading of levels of carbon monoxide, which is an odourless, colourless gas that can be emitted by furnaces, wood stoves, and barbecues.
The gas is toxic in high concentrations.