Tucson firefighters treat a dog that suffered carbon monoxide poisoning Sept. 26, 2017 at a house on the west side, said Capt. Andy Skaggs of Tucson Fire Department. A grandmother and her two grandchildren were taken to a hospital for treatment. 

A grandmother and two of her grandchildren were taken Tuesday night to a hospital after showing signs of carbon monoxide poisoning.

Their conditions were not known late last night, said Capt. Andy Skaggs, a Tucson Fire Department spokesman.

Tucson firefighters responded to the 2500 block of West San Marcos Boulevard on Sept. 26 shortly before 7 p.m. for reports of the poisoning by the odorless gas, said Skaggs.

The neighborhood is west of South La Cholla and south of West Starr Pass boulevards.

Firefighters found a grandmother in her 60s, along with her grandson, 16, and her granddaughter, 18, in the house showing signs of carbon monoxide poisoning, Skaggs said. A family dog also showed signs of poisoning.

The three were taken to a hospital for treatment, and the dog was treated with oxygen at the house, Skaggs said. The mother of the teen boy and younger woman arrived at the house and found the three ill, and called 911.

Firefighters determined a vehicle in the garage was accidentally left running with the garage door closed, but the door to the house was open. This allowed carbon monoxide into the house.

Carbon monoxide is described as a "silent killer" because it is an odorless, colorless and tasteless gas that is virtually undetectable, Skaggs said. A person breathing it may lose consciousness and not be able to escape.