The fire at 16th and Market Streets struck an apartment building full of sleeping people.
"It was really scary to hear people yelling 'fire, fire.' It was really frightening," said victim Patrick Fowler.
Residents made it out safely to the street -- then some of them used their cell phone cameras to capture the fire. Thirteen people lost their home.
"It shot up pretty high for a little bit," said victim Todd Suchevits.
"How are you emotionally?" asked ABC7's Amy Hollyfield.
"Fine, shocked - and just glad that everyone made it out," said Suchevits.
Firefighters called for a second alarm -- so all available crews in the area were working to put this fire out -- when another call came in for a fire just a few blocks away. Firefighters had to ask for help from across the city.
A fire at 17th and Hartford also involved a residential building, but it's under renovation - so no one is living there. It did threaten the building next door.
"I went and checked on the back window and looked next door and the whole back of the building was on fire. So we just got out," said victim Brian Kendall.
Firefighters called arson investigators as soon as they put out the fire.
"The first thing we thought about being suspicious - you had two fires within a block of each other within an hour," said SFFD Dep. Chief Pat Gardner.
Firefighters aren't the only ones with their suspicions.
"The power switch is right there and so there is no power to the building and there is no power in the corner of that building. So it is clear that someone did this," said the owner of the building at 17th and Hartford.
The owner of has spent the last six months renovating the historical building on 17th.
No one was injured in the fires.