Plenum Rated Cable

Q: We have decorative wood panels in our cafeteria ceiling which do not provide a seal to limit the passage of smoke. In fact, there are wide gaps between the wood panels. HVAC supply ductwork is mounted above the wood panels and return air is drawn through the open space above the wood panels as well. Are we required to use plenum rated cabling above the wood panels?

A:  The Life Safety Code, 2000 edition, section 3.3.150 defines a plenum as a compartment or chamber to which one or more air ducts are connected and that forms part of the air distribution system.Given that the above-ceiling space is used as a chamber for the return air of the HVAC system, the space appears to be a plenum and I would conclude that plenum-rated cable should be used. NFPA 70 (1999 edition), section 300-22(b) specifies that Type MI or Type MC cable must be installed in ventilating air plenums. This standard does allow limited lengths of flexible metal conduit and liquid-tight flexible conduit to devices permitted to be in the plenum.

Ceiling Resisting the Passage of Smoke

Do the ceiling tiles in these pictures look anything like what you may have in your hospital? If so, then you may be out of compliance with the Life Safety Code. The ceiling, no matter what it is made of, is required to ‘resist the passage of smoke’, according to the Life Safety Code.

The logic behind this requirement is if a fire were to start in a room with sprinklers or a detection system, the ceiling must ‘resist’ the smoke from traveling up to the interstitial space above the ceiling. That way the heat and smoke will travel along the ceiling and activate a sprinkler or a detector. If the ceiling does not ‘resist’ the passage of smoke, then the heat and smoke would bypass the suspended ceiling and delay activating the sprinklers or detectors.

 

When the facility is protected with sprinklers or a fire detection system, the ceiling is required to resist the passage of smoke. An acoustical suspended ceiling with tiles and a grid, have been identified in the Life Safety Code as meeting the requirements of ‘resisting the passage of smoke’, even if the ceiling has speakers and light fixtures.

Now, a missing ceiling tile or a hole in an existing ceiling is pretty obvious, and most people would agree those tiles would not be able to resist the passage of smoke. However, an IT cable run along the wall up to and through the suspended ceiling with the tile setting slightly ajar may not be as obvious. But this is just as bad as a hole in the tile or a missing tile all together, as the tile cannot properly resist the pasasage of smoke. It’s not properly seated in the grid.

If you have a temporary situation that requires IT cable for just a day or two, you could probably get by without cutting the tile or grid by using an Interim Life Safety Measure (ILSM). But for longer installations, it is best to properly install surface mounted raceway, like Wire Mold and properly trim the ceiling tile and grid to continue to resist the passage of smoke.

 

Missing escutcheon plates (escutcheon plates are the trim rings around the exposed sprinklers or cover plates over the recessed sprinkelrs) are just as bad as missing or broken ceiling tiles, as they no longer resist the passage of smoke. Without the escutcheon plates, smoke and heat will bypass the sprinkler and the activation of the sprinkler will be delayed.

Take a look at your acoustical tile and grid suspended ceiling system through-out the hospital. If you find cracked, broken or missing tiles, or tiles with holes, or untrimmed tiles, or sprinklers with missing escutcheon plates, you need to resolve those problems before a surveyor or an inspector cites you for it.