THE BENDS AND DIVING BELL IN THE NORTH SEA

In the memoir I talk about decompression chambers on oil rigs in the North Sea.

Before the use of the decompression divers had to decompress on a divers cage suspended in the North Sea to avoid the bends. Decompression sickness, or "the bends," is a serious, sometimes fatal condition resulting from a rapid decrease in surrounding pressure, It occurs when nitrogen absorbed into the body under high pressure forms bubbles in tissues and blood upon fast ascent, similar to opening a carbonated drink. The most common symptom is Intense joint/bone pain (which gives the condition its name).

The diver would be brought up on the cage  to a reduced depth, therefore reduced pressure. Where he would remain for long enough for the bubbles to leave the body. He would then be brought up to another level where the process was repeated.

In the North sea the temperature in Winter is 5 to 9C and the decompression would take several hours, not a pleasant experience. Divcon, the company I worked for introduced the use of the diving bell . The Bell would be taken down to the same depth as the diver. With the bottom half of the bell pressurized up to the pressure at the diver’s depth the diver would be l locked into the lower chamber, the diving bell brought up to the surface and the diver locked into a decompression chamber on the oil rig which had been pressurized up to the same pressure as the lower half of the diving bell. The pressure in the decompression chamber was then reduced  in stages. The diver could relax in relative comfort and read, the  most favorite material being comics. Often to decompress the chamber had to  pressurize up to a higher pressure than the diving bell. In extreme cases when this was not possible the diver had to be brought up to a hyperbaric chamber belonging to the British Navy by helicopter. The process Taking a diver suffering from the bends  in a helicopter can cause their condition to severely worsen or become fatal if not handled properly.

When a diver with decompression sickness (DCS) is exposed to a lower-pressure environment, such as the high altitude of a helicopter, as the  helicopter ascends, it causes  the ambient pressure to decrease. This causes existing nitrogen bubbles to grow larger and new bubbles to form, which can worsen joint pain, create neurological symptoms (numbness, paralysis), or cause pulmonary DCS ("the chokes").

While helicopter transport is risky, it is often necessary to get the patient to a hyperbaric chamber quickly. The danger of worsening the condition must be balanced against the need for rapid, definitive treatment. To reduce this risk, emergency protocols for helicopter transport of divers include: Helicopters should fly as low as possible, preferably not higher than 300 meters (1000 feet) above sea level, to keep ambient pressure as high as possible The diver should be given 100% oxygen during the entire flight to help reduce bubble size and treat the condition. The patient is typically kept in a horizontal or slightly reclined position, rather than upright, to prevent bubbles from traveling to the brain.

The use of heliox in diving has a number of benefits.  At depths beyond approximately 40 meters (130 feet), nitrogen in regular air begins to have a narcotic effect on divers, similar to alcohol intoxication. By replacing nitrogen with helium (which is non-narcotic at these pressures), divers remain mentally alert and clear-headed, enabling them to work effectively and safely at greater depths.

Helium is a much lighter, less dense gas than nitrogen. As a diver descends, the ambient pressure increases the density of the breathing gas. The lower inherent density of heliox means less effort is required to move the gas in and out of the lungs, which reduces respiratory muscle fatigue (work of breathing) and improves ventilation.

Helium is less soluble in body tissues and diffuses faster than nitrogen. This property can lead to different decompression profiles and potentially a reduced risk of decompression sickness  used correctly with appropriate decompression schedules  for heliox must be followed.