Fire Testing
of
Communications Cables
in
Plenums

Presented by: Loren Caudill, DuPont, to the International Fire Safety Conference in San Francisco in 1996.
Sponsored by: The Society of Plastics Industries, Inc.
Participating Companies: AT&T Bell Laboratories, Ausimont, Daikin, DuPont, Elf Atochem, and Solvay Polymers
 

In response to increased specified activity relating to fire testing of wire and cable with the international community, a study was conducted at the Building Research Establishment / Fire Research Station in Cardington, UK by the Fluoropolymers Division of The Society of the Plastics Industries to investigate and compare the fire performance of a range of communications cables installed in concealed (plenum) spaces. These horizontal spaces include the area above a suspended ceiling and under a raised floor.

CONCERN ABOUT BUILDUP OF COMBUSTIBLES IN CONCEALED SPACES (PLENUMS)
The rapid growth of computers on local area networks (LAN) and the complete replacement of cables approximately every 2-3 years has led to a concern about the accumulation of combustibles in these spaces. These concealed spaces can provide a path for fire and smoke to spread undetected throughout a building.

All the cable /trunking conditions tested in this study would be acceptable under current UK guidelines. Only the CMP cable and the CMX cable in trunking would be acceptable in the US. The results of this study demonstrate the different levels of performance between UK and US practices. Of the cables tested without trunking, only CMP cable has performance equivalent to CMX in trunking.

The need for an International Fire Test Standard for communication cable installations is being studied by IEC SC20C (flammability of wire and cable) and data from this work will provide guidance.

A Test Program was developed utilizing full-scale and intermediate scale testing. The cables tested were 4 pair UTP (unshielded twisted pair) communication cables. There were 200 lengths of cable used per test. This represents one generation of cable in a typical open-plan office installation.

FULL SCALE TESTING
For the full scale testing, a reburnable test rig was constructed at the Building Research Establishment / Fire Research Station in Cardington, UK This facility was chosen because of its capability and reputation as one of the premier fire testing laboratories in the world.

• The test rig consisted of a concrete block building with external dimensions of 7.37 meters in length by 5.7 meters wide. The height of the rig was 4 meters with a drop ceiling forming a concealed space 1 meter deep.
• Two extract systems were fitted: a low volume extract system exhausting into a small 150 mm diameter duct, and a high volume extract system, having a speed controlled extract system having an extract rate up to 4.5 cubic meters/sec exhausted into a large duct 760 mm in diameter. Both fans (one on each duct) were of the bifurcated type. For this study, the small duct was blocked off so that all flow was through the large duct
• Cables were supported on steel ladder 7.2 meters long by 380mm wide. The ladders were installed in the center of the concealed space through an opening in the end of the wall.
• A high fire performance (2 hour endurance) ceiling was installed with a breach arrangement directly over the fire source. The fire source consisted of kiln dried pinus sylvestris with approximately 20% moisture content and stored in a conditioned room until used. The average crib stick dimensions were 60mm by 60mm by l meter. A total of 100 sticks were used to generate a 1 megawatt fire.
• All cables were stored in a conditioning room at 23 degrees centigrade and 50% relative humidity for a minimum of 10 days.
• Thermocouples (30-40 per test) were placed throughout the burn room in the concealed space and in the exhaust duct. This allowed for vertical and horizontal mapping of the temperatures and served as a means to determine flame spread along the ladder in the concealed spaces.
• Gas Sampling for O₂, CO, C0₂was used for calculating the heat release rates and determining the type and stage of the fire.
• Smoke and velocity measurements were taken in the exhaust duct.
• For calibration purposes, an insulated board was placed on the ladder and thermocouples were Installed along the board to obtain a background profile without combustibles.
• Videos of the burn room and the concealed space were recorded for each test Also still photos were taken every 1 minute. These provided the visual analysis of the burn tests.
• All data was collected electronically every 10 seconds for on-line real time monitoring and the data was stored in a spreadsheet format.

Cable Description
The products tested consisted of the following commercially obtained cables and trunking.

• CMX - PVC / PE
• CMX - PVC / PE in trunking
• LSF - Low Smoke / Fume Non-Halogen
• CMP - Fluoropolymers

CMX in metal conduit is the requirement in the National Electrical Code in the United States and was the benchmark for the CMP cables that are allowed now.

TEST RESULTS

Total Heat Release Measurements
Cable ID	Full-Scale	NFPA 262
CMX/Trunking	13	109 109
CMX Exposed	610	241 234
LSF Exposed	457	248 244
CMP Exposed	68	141 119

                                          

Relative Ranking
	Flame Propagation	Smoke Generation	Total Heat Released
CMX/Trunking	1	1	1
CMP Exposed	1	1	1
LSF Exposed	4	2	4
CMX Exposed	4	4	4

CONCLUSIONS

• Of the exposed cables tested, only exposed CMP (fluoropolymer) cable showed fire performance comparable to CMX (PVC/PE) cable in cable in metal trunking.

• The Steiner tunnel test (NFPA 262) correlates well with full scale results from Building Research Establishment/Fire Research Station.