John Bennett dived to 254m open-water dive in the Philippines in which 41-year-old Briton John Bennett set a world record depth. The dive beat by a large margin the previous record of 202.5m, set in March by Belgian Ben Reymenants at Dahab in Egypt.
Backed by a team from Capt'n Gregg's dive centre at Puerto Galera, Oriental Mindoro, Bennett dived on open-circuit trimix to a carefully planned schedule aimed at providing new parameters for deep diving in general.
Using a custom-prepared dive profile on Abyss software, Bennett employed very slow ascents and, during decompression, a relatively new technique called back-switching, in which the diver regularly switches from pure oxygen to the leanest oxygen mix allowed at that depth, to limit potentially dangerous exposure to high levels of oxygen.
Bennett took the technique one stage further by back-switching to pure helium for periods during decompression at the top stops, and is convinced that this was the single most important aspect of developing a safe deep-dive decompression routine. He reported no problems with decompression illness, oxygen hits or HPNS (a nervous system complaint linked with rapid descents to depth).
Bennett used four trimixes: 16/48 on the descent to 90m; 4/80 bottom mix from 90m down and back up to 150m; 10/69 from 150m to 90m; 16/48 again to 60m; and 23/23 to 39m. From here he used nitrox mixes of 33 per cent to 21m, 50 per cent to 12m and 73 per cent to 6m, from where he finished decompression on pure oxygen. Switchovers were extended over a period of time to ensure that his body did not react to a rapid change of gas.
Bennett's descent rate was 25m per minute, the ascent 25m/min to 180m, 15m/min to 150m, then 10m/min. He did 30-second stops every 10m from 150m to 120m, then one-minute stops from there to the surface.
For the dive a weighted line was set and PADI course director Alan Nash, an independent observer, witnessed Bennett return to the surface with a tag that had been set at 250m. After analysis of the dive computers and allowing for some line stretch, the depth of 254m was agreed.
