Final answer:
During a dive, if TLC falls below RLV, pulmonary air pressure exceeds external water pressure, leading to potential DCS. Divers must ascend slowly and use a BCD to control buoyancy and pressure. Barometric pressure variations, like those found at high altitudes, increase the risk of DCS.
Step-by-step explanation:
If TLC (threshold limit value) during a dive drops below RLV (residual lung volume), pulmonary air pressure becomes more than the external water pressure. This is due to the variations in barometric pressure experienced during a dive. DCS (decompression sickness), also known as 'the bends', can occur if a diver ascends too quickly from depths where the water pressure is much higher. At depth, the great pressures from the water column cause the air within a diver's body to be at a higher pressure than the surrounding water. As a diver ascends, the pressure decreases and the air expands according to Boyle's law, which can create problems if the ascent is not controlled and the pressure equalization is not adequately managed.
To avoid DCS, divers must ascend slowly and make decompression stops when necessary. The use of a buoyancy compensator (BCD) is crucial for controlling ascent and descent during the dive to maintain the correct balance between the internal pressure within the diver's body and the external water pressure. Proper training and following safety protocols can help avoid serious risks.
Lastly, the ambient pressure at the surface can also affect the likelihood of DCS. For example, diving in deep mountain lakes, where the barometric pressure at the surface is less than at sea level, increases the chances of DCS because of the additional pressure reduction upon ascent.