The apartment building on Sterlingshire at Mesa started to burn around 10pm.
A woman who uses an oxygen machine says she reached for her cigarette lighter and lit it multiple times, causing the oxygen tank to catch fire.
The woman yelled for help and her son ran into the bedroom, grabbed her and took her outside.
Her son then ran back into the burning building to get his mom's portable oxygen tanks.
Four units were heavily damaged by the fire. Six additional units received smoke damage, but no one was hurt.
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