SUPPRESSION OF ELECTRICAL CABLE FIRES: DEVELOPMENT OF A STANDARD PVC CABLE FIRE TEST FOR ISO 14520-1

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SUPPRESSION OF ELECTRICAL CABLE FIRES
DEVELOPMENT OF A STANDARD PVC CABLE FIRE TEST FOR
ISO 14520-1
Mark L. Robin Hughes Associates,
Inc. and Thomas F. Rowland, James Harris and
Vimal Sharma Great Lakes Chemical Corporation
Presented at 2002 Halon Options Technical
Working Conference April 30 - May 2,
2002 Albuquerque, New Mexico
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ISO 14520 Gaseous Fire Extinguishing Systems

• ISO 14520 Class A Task Group
• Wood Crib
• Plastics
• Cable Tray
• PVC Cable Tray
• ISO/TR 20885 Proposal

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ISO/TR 20885 Cable Tray

• Perforated Cable Tray
• Swifts Medium Duty MRFL/25/PG
• 750 mm length x 225 mm width

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ISO/TR 20885 Cable

• 10 PVC cables per tray, RS 366-823
• 750 mm length
• spaced 10 mm apart
• Six cable trays stacked on top of each other

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ISO/TR 20885 Specification
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ISO/TR 20885 Ignition

• Ignition
• 200 mm x 200 mm x 20 mm SS pan filled with 100 mL
  heptane
• Provides 90 seconds preburn

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ISO/TR 20885 Procedure

• Six stacked cable trays, 10 lengths PVC cable per
  tray
• 90 second heptane preburn
• Agent released at 270 seconds
• Fire size 20-30 kW typical
• 10 minute hold period

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ISO/TR 20885 Pass/Fail Criteria

• Flames extinguished within 60 seconds from the
  end of discharge
• Currently under debate by task group
• No reignition upon exposure of cable tray to
  atmosphere after 10 minute soak

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ISO/TR 20885 Test Configuration
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ISO/TR 20885 Problems

• Reproducibility
• Heptane preburn
• Fire characteristics
• identical cable different results
• attributed to experimental configuration

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ISO/TR 20885 Problems

• Specifications
• Cable from sole manufacturer
• Cable tray from sole manufacturer
• availability problems in certain regions
• single source problems

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ISO/TR 20885 Problems

• Cable Tray
• Single source specified
• Perforated cable tray uncommon in US

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ISO/TR 20885 Problems

• Configuration of Cable Trays
• Stacking of cable trays on top of each other not
  encountered in field
• NEC requires adequate space around cable tray to
  allow servicing

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Cable Tests Standards

• Large-Scale
• BS 4066, Part 3 1994
• 3.5 meter cable lengths, vertical orientation
• IEEE 1202-1991
• ASTM D-5337
• UL 1658
• all involve 2.4 meter cable lengths, vertical
  orientation

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Cable Tests Standards

• Small-Scale
• BS 4066, Part 1 1980
• single strand, 675 mm in length, vertical
  orientation
• UL 1581
• 460 mm specimen, vertical orientation

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Cable Tests Industry Studies

• Sumitra
• Horizontal and vertical arrangements
• Ladder-type tray
• Horizontal arrangement
• 12 Cable trays stacked with 10.5 spacings
• 8 foot long cable trays, 18 wide x 3 deep
• Heptane ignition
• Suppression by water

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Cable Tests Industry Studies

• Chavez, et. al.
• Ladder-type tray
• Horizontal and vertical configurations
• Horizontal configuration
• two or five stacked trays, 10.5 spacing
• Propane burner ignition
• Suppression by water, CO2 , Halon 1301

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Cable Tests Industry Studies

• Sumitra and Chavez, et. al.
• Insight into effects of
• Cable type
• Cable loading
• Cable arrangement
• Ignition source
• Etc.
• Large Scale Expensive

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Cable Tray

• Ladder Cable Tray
• employed in majority of cable tray wiring system
  installations
• permits maximum free flow of air across cables
  efficient heat dissipation

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Cable Tray

• Ventilated Trough Cable Tray
• Cable Tray Institute Only reason to select a
  ventilated troughcable tray over a ladder type
  cable tray is aesthetics
• No drooping of small cables visible

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Cable Tray

• Solid Bottom Cable Tray
• Selected where concern exists for EMI/RFI
  shielding protection for very sensitive circuits

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Development of a PVC Cable Test

• Ladder Tray
• employed in majority of applications
• Horizontal Stacking
• 12 to 18 spacings recommended
• Reproducible fire
• Reproducible suppression
• Simple, Cheap

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PVC Cable Test Configuration
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Specification of Test Parameters for PVC Cable
Fire Test
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Composition and Cone Calorimeter Data for Cables
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Fire Size at Agent Discharge
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Conclusion

• Test protocol developed for PVC cable fires
• Reproducible fires
• Reproducible suppression
• Specifications proposed for cable, cable tray
• Simple, relatively inexpensive method
• Protocol to be submitted to ISO 14520-1 committee
  for consideration