The plenum areas within a data center present unique challenges when it comes to protecting against fire. These oxygen-rich hidden areas within dropped ceilings or under an elevated floor manage return airflow to HVAC equipment and house vast networks of plastic-coated mechanical pipes and cabling. Material combustibility and the toxicity of plastics and various wrappings when exposed to flame have led to changes in codes and the development of materials suited for the plenum space.
Sadly, history bears out the potential threat these spaces provide. A February 1975 fire at the World Trade Center in New York was linked to cables installed in plenum spaces and led to changes in codes governing plenums. A New York Board of Fire Underwriters report stated, “The worst and most hazardous condition is when wires and cables with combustible insulation are run through plenums to service the floor above. This provides a double hazard by introducing combustibles into the air conditioning. It should be noted that the mass of cables to supply communication equipment in many office occupancies is sufficient to sustain a substantial fire. While an individual cable is extremely difficult to ignite, a group of cables lying parallel will burn intensely, similar to the situation that exists with a group of logs in a fireplace.”