Chapter 5.2.7.1 - Safety Issues

The safety concerns raised by concealed-element failure resulted in a comprehensive
review by the Canadian Standards Association and Underwriters Laboratory. Product
testing, installation, and application listing standards were subsequently revised. The
most significant factor for design was a reduction in element wattage per square foot
of flexible or rigid ceiling panels, which means that more ceiling space and more elements
are now required to compensate for the resulting drop in element temperature.

It was found that when gypsum board is subjected to long periods of continuous
heat, the moisture content drops to a point at which gypsum becomes a heat insulator
rather than performing the heat conduction function as designed. Testing also
found that some of the elements were electrically unstable and evidenced declining
resistivity and increasing heat output over time.The information developed has led
to a reduction in maximum element wattage output.The result is a reduction in element
temperature and therefore a reduction in the maximum temperature to which
the gypsum ceiling board may be exposed.

The product classification and application listing changes reduced maximum element
wattage output and gypsum ceiling panel temperature. This correspondingly
increases the area of a ceiling, other things being equal, that would need to be covered
by the element to provide the wattage required to meet the heat loss.The interested
reader is encouraged to obtain current information from the CSA, UL, ETL,
and product manufacturers prior to designing a concealed electric radiant ceiling
panel heating system.

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