HAZARD ALERT - LIGHTWEIGHT STAIR CONSTRUCTION.
3/4" OSB and Gusset Plate Constructed Materials
Not like fighting a basement fire wasn't dangerous to begin with, but now us brother and sister firefighters need to worry about the structural integrity of what contractors and/or engineers feel are "lightweight stairs"
You see instead of using 2x12" stringers, this new lightweight constructed staircase is made with a 2x4 running the entire length of the staircase (on the side) where the 2x12 stringer would normally be. The triangles you see are providing the actual strength for both the risers and treads. This lightweight system is held together by glue and nails.
The treads and risers are made up from 3/4" OSB. It is reported in a main staircase (1st to 2nd floor) the underside of the stairs would be covered with drywall for added fire protection. When used for an unfinished basement installation, the stairs would be left as seen above (non-protected)
In the photo below the first two treads were upgraded or replaced with a hardwood tread cap. Note the top two treads are still OSB with square cut leading edges. In either configuration, the riser remains OSB and the treads are supported via the lightweight steel triangles.
When the stairs are trimmed out in detail (either carpet or hardwood) they are difficult to identify and determine if they are "traditional stringer or lightweight" construction as seen below. Most commonly found with carpet covering them.
It has never been more important to discuss basement fire operations with your firefighters. The focus should be on a solid size up of the dwelling, the age, construction type and materials that are typical for that dwelling, where is the fire, what is burning and how long has it been burning before we arrive? Newer lightweight dwellings with a well involved basement fires are Born Losers! Do not fall into the trap.
Remember if you decide to go interior, the use of your (TIC) thermal imagining camera should only be used as a tool from your toolbox and NEVER rely solely on that one sense of sight through the camera. Our FETC Interior Benchmarking class discusses the use of tools to increase your situational awareness by combining them along with our senses of what do I see, feel, and hear. The Underwriters Lab (UL) has done a great study on basement fires and how different types of flooring materials may mask the actual temperatures viewed on a TIC. Surprisingly even with the use of lightweight materials under foot!
The traditional tactic of sounding the floor has never been more important! Make sure you are sounding the floor in front of you while you make the next advance!
Take Care and Stay Safe...