15-17 FIRE ZONE CONSIDERATIONS

FIRE ZONE CONSIDERATIONS

Every effort shall be made to eliminate any fire hazard within a chamber. When oxygen percentages are elevated as during the later stages of decompression, a fire will burn rapidly once started, perhaps uncontrollably. As a result, special precautions are necessary to protect the diver’s safety when in the fire zone. The fire zone is where the oxygen concentration in the chamber is 6 percent or greater. Using standard saturation diving procedures (oxygen partial pressure between 0.44 and 0.48 ata), fire is possible at depths less than 231 fsw. Thus, during a saturation dive the divers will be in the fire zone during initial compression to depth and during the final stages of decompression.

Example. The chamber atmosphere is 0.48 ata ppO2. The minimum oxygen percentage for combustion is 6 percent. Compute the fire zone depth.

The fire zone depth is computed as follows:

        PPo2   * 33      
Fire zone Depth(fsw)   =   ------------ - 33
        o2 %  / 100

        0.48   * 33      
     =   ------------ - 33
        0.06

    = 231  fsw      
Although the design of the DDS minimizes fire potential, personnel must remain vigilant at all times to prevent fires. Appropriate precautions for fire prevention include:

  • Fire-suppression systems, if available, must be operational at all times when in the fire zone.
  • Chamber clothing, bed linen, and towels shall be made of 100% cotton. Diver swim trunks made of a 65% polyester–35% cotton material is acceptable.
  • Mattresses and pillows shall be made of fire-retardant material when in the fire zone.
  • Limit combustible personal effects to essential items.
  • Limit reading material, notebooks, etc., in the fire zone.
  • All potential combustibles shall be locked in only with the permission of the Diving Supervisor.
  • Whenever possible, stow all combustibles, including trash, in fire-retardant containers, and lock out trash as soon as possible.
  • Being thoroughly familiar with all emergency procedures (EPs) regarding fire inside and outside the Deep Diving System.

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