INCIDENT REPORT #1 – Failure of BCD

Nature of Problem: Failure of BCD

Halfway out of Mayor’s Chamber of HERUC (Hinatuan’s Enchanted River Underwater Cave), my BCD suffered a leak through the purge valve. Four FCD’s use Hollis SMS 100 in the sidemount configuration. Out of convention, the power inflator and the purge valve were switched positions:

inflatorandpurge

Fig 1. Side-by-side, Hollis® SMS 100 in conventional power inflator and purge valve (left), and switched positions (right).

Figure 1, right shows the purge valve mechanism on the left shoulder. At first glance, this would not cause any problem. However, in the limestone dissolution cave environment, an unforeseen problem of pieces of limestone falling from above as they are dislodged by the bubbles in open circuit diving, proved to be problematic.

The Exit from HERUC and the Deco Stops

I literally had to crawl out of HERUC. As luck would have it, during the planned deco stops, Enchanted was current-neutral. (I have dived the area with a hefty down current at the height of the flood stage of a spring tide).

rockclimb

Fig 2. Docboy “rock climbing” on the deco stops with FCD Andy keeping a close eye

Problem Analysis

After an uneventful completion of the deco schedule, analysis revealed a small speck of limestone lodged under the purge valve lid causing the free-flow. The Hollis® SMS 100 is unprotected on the shoulder position. In the conventional configuration, it is well protected in the left hip area. Incidentally, the Hollis® SMS 50 purge valve is around the left shoulder area, but securely protected by the bladder.

speck

Fig 3. A 2-mm speck of limestone, the kind that “rains” on the divers as porous limestone is dislodged by the bubbles of open circuit diving

Hindsight Solutions

Either one will do:

  1. Position the power inflator and purge valve in conventional manner – power inflator on the left shoulder, the purge valve tucked under the bladder in the left hip area
  2. Redundant bladder with independent power inflator

Article by:

Dr. Alfonso Y.  Amores

Dr. Alfonso Y. Amores

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