PORTLAND, Ore. (KOIN) — The abandoned commercial building that caught fire and collapsed in Southeast Portland September 24 had a giant “U” posted on the outside. That is the designation for a building that, in the event of a fire, the building is unsafe for firefighters to enter.

There are only about 60 buildings marked with the “U” throughout the city, said Portland Fire & Rescue spokesperson Terry Foster. The designation does not mean they are unsafe to patronize businesses that may be inside, only that firefighters must be extra careful in the event of a blaze.

“Some of these buildings that are deemed unsafe are still occupied for businesses and things like that, but if it’s an immediate danger to people, we can go through the process of ‘Hey it’s not even safe for you to be in this building’ and we need to work on that,” Foster told KOIN 6 News.

When the 4-alarm fire near Southeast 9th Avenue and Alder began, there were already floors missing, he said. Audio recordings that day showed fire crews went into the basement of the building but quickly left when conditions deteriorated.

A building can be marked with a “U” for a number of different reasons, such as not enough exits, the age of the building or structural deficiencies.

​”There’s a reason we have those codes, like a certain amount of exits and if those get changed without using the permit process that can be deemed an unsafe building,” he said.

The investigation into the cause of the fire is in the early stages. Crews from ATF and Portland police joined PF&R. Foster said it will be a process to determine the cause.