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RE: Swimming pools

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>From Engineering News-Record, June 13, 1985:

"The corrosion of stainless-steel hangers has been confirmed as the main 
cause of the collapse of a swimming pool ceiling ... last month.  The hangers 
suspended a concrete ceiling below the roof framing.  The accident killed 12 
swimmers and injured four."

"A report ... cited the cumulative effect of 13 years of exposure of the 
steel to chlorine vapors.  The institute called the phenomenon 
'transcrystalline tension crack corrosion.' "

"There was no suggestion that the AISI No. 304 hangers were defectively 
installed or not up to specification.  This commonly used type of stainless 
steel is resistant to corrosion in many environments, but it is not immune,"

"Chloride was found even in the smallest cracks of the slab.  Air from the 
pool area was recirculated through the space between the roof and the 
concrete slab, bringing chlorine into continuous contact with the hangers."

Hope this helps.  (Never in a million years will I find what I am looking for 
in the first place I look!)

A. Roger Turk, P.E.(Structural)
Tucson, Arizona