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    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 adequate materials for "lightweight stairs".  We all understand that when a dwelling is being built, fire protection is not the utmost priority.  For us firefighters, it would seem as though it should be but time and money are factors that drive the industry.  Frank Brannigan always preached, "Know Your Enemy" relating to building construction. So this hazard alert is based from a firefighter's view reference to firefighter safety.  The concern was first presented to me from a good friend in the industry about two years ago. Over that period of time, I had not been seen them used in the industry. Now a few months later they are starting to be more prevelant in areas where newer, lightweight homes and/or multi family structures are being built.
I will start off this piece with a photo of a standard wood-framed "stringer, riser and tread" to refresh our memory of how traditional stair assemblies are built. ( see left)
Now with the new lightweight stair assembly, instead of using traditional 2x12 stair stringer, this new lightweight constructed staircase is made with a 2x4 running the entire length of the staircase (on the side) where the standard stringer would normally be.  The triangles you see (photo below) 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 located, what is burning and how long has it been burning before we arrived?  Newer lightweight dwellings with a well involved basement fire 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... Hey remember to check out more great information from the author on "Tap the Box with FETC" on Fire Engineering Blog Talk Radio.

Billy Greenwood
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Comment by Jeffrey A Frommeyer on May 21, 2014 at 11:18am

Specifically, what municipality or engineer would approve this type of construction?  

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