(CNN)--One firefighter died and another is in critical condition after battling a four-story house fire in San Francisco.
This is video from the hospital.
A department spokesperson says there was a huge flash inside the home.
It apparently triggered the heat alarm on one of the firefighter's uniforms.
Additional crews went inside and found them with severe burns.
A third injured firefighter made it out on his own.
There's no word on what sparked the fire.
Warmer, more humid, and unsettled weather pattern develops next week.
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