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### Danger of Opposing Fire Streams Danger of opposing fire streams does exist, however, from interior lines. It is even possible in core-construction techniques for a single hoseline to drive fire around the core and back on itself. In this design, there is often a common corridor that wraps compl...

### Danger of Opposing Fire Streams Danger of opposing fire streams does exist, however, from interior lines. It is even possible in core-construction techniques for a single hoseline to drive fire around the core and back on itself. In this design, there is often a common corridor that wraps completely around the core, connected by the elevator lobbies (see fig. 18-34). A single hoseline equipped with a fog nozzle, advancing out of a stairwell in one direction can push fire around the corridor and right back toward the open attack stair door, almost like a dog chasing its own tail. The resulting heat coming from the rear can force the attack line to retreat rapidly to the stairway The only solution may be to fight your way out of the stairway with two lines: one to advance and one initially to remain at the stairs to protect the rear. ### Another common problem with core construction Another common problem with core construction is the presence of scissor stairs, which alternately exit the core on opposite sides. It will be necessary in this case, when staging for operations on the floor below the fire, to set up and connect to the standpipe on the side of the building that is opposite the fire. Be aware of the danger of a second hoseline operating out of the other staircase from two floors below the fire (the next available standpipe outlet) and driving fire back around the core at the first line (fig. 18–37). An additional type of stairway commonly found in high-rise building is called an access stair. This is usually an open, unprotected stairway leading from floor to floor within a single-tenant occupancy (fig. 18-38). ### Common problem with businesses in rentals It is common for businesses to rent more than one floor. The public exit stairs are usually designed not to allow reentry on any floors aside from the ground-floor exit or other specific floors. In this case, if an employee wanted to take a form to another floor, it would be necessary to go out to the public lobby and take the elevator up or down, then reenter. This is a very common arrangement for security reasons. To avoid waiting for elevators and having to travel outside the office, an extra convenience stairway is often added. Since it isn't a required exit, it is often unprotected. From a fire protection point of view, it is a nightmare. The slightest amount of smoke will almost immediately trigger alarms on all of the connected floors. If a serious fire develops, the available floor area doubles or triples, and with it, the threat to life.