A reverse block is a condition in which the breathing gases in a scuba diver’s airway are prevented from leaving the lungs by an obstruction. The most common causes of reverse blocks are regulator failure, poor dive planning or poor buoyancy control. As the name suggests, this means that after exhalation, instead of the breathing gas being released into the water as bubbles, it is trapped within the diver’s body and cannot escape. If left untreated, a reverse block can lead to pulmonary barotrauma (lung over-expansion injury), which can be fatal.
A reverse block can be caused by many different scenarios. Often, however, because of regulator failure, poor dive planning or poor buoyancy control.
The regulator may be blocked by water or a foreign object that is blocking the air flow at the mouthpiece. This will cause an increase in pressure in the mask and your lungs (and ears), which can lead to ear barotrauma, lung over inflation and other injuries. If this happens to you on a dive then you should try removing any object that is blocking your breathing equipment as soon as possible as it could become more difficult to remove once your body becomes accustomed to having less pressure around it due to being under water for some time already and being able to hold onto something while trying not do drown yourself!
After exhalation, instead of the breathing gas being released into the water as bubbles, it is trapped within the diver’s body and cannot escape. This occurs because of a difference in pressure between the inside and outside of your lungs.
If you are diving on air (which contains 78% nitrogen), there is no problem if this occurs because nitrogen dissolves into body tissues at a concentration far lower than its saturation pressure (if you breathe pure nitrogen it will form bubbles). However, if you are diving on compressed air or nitrox then there is more oxygen dissolved in your blood compared to nitrogen so any trapped gas has less room to expand and can still cause blockage even if you continue breathing normally.
If left untreated
If left untreated, a reverse block can lead to pulmonary barotrauma (lung over-expansion injury), which can be fatal.
Pulmonary barotrauma is caused by the over-expansion of the lungs, which can be a result of an increase in air pressure.
It’s not uncommon for divers to experience this injury while completing deep dives. The most common symptom of pulmonary barotrauma is difficulty breathing or chest pain, which many people mistake as a heart attack or stroke. If left untreated, this condition can lead to death.
If a regulator is suspected to have caused the blockage, it should be removed from service for immediate inspection. This occurs when one or more divers report difficulty breathing and/or feel pain during the dive.
Inspect for damage. Look for any physical damage on the surface of the regulator that could be related to an internal blockage. If there is any doubt about whether or not your equipment is safe, do not use it until you have been able to inspect it thoroughly. Many manufacturers require that you send them your gear in order to have it inspected by their technicians, who can often determine if there has been damage caused by improper maintenance or other factors unrelated to normal wear-and-tear that may cause internal blockages..
Replace if damaged: If you find any evidence of physical damage (even if only slight), replace your equipment immediately because—like most things in life—your regulator will likely get worse before getting better and could lead you into dangerous situations should something go wrong while diving with an unrepaired regulator which could result in injury or death!
Always exercise caution when using a regulator
If you experience a reverse block, it is important to ascend immediately. If you are unable to ascend, release air from your BCD and inflate your vest. You should also try to clear the blockage by exhaling forcefully through your regulator.
A reverse block is a serious condition that can lead to pulmonary barotrauma and even death if left untreated. Scuba divers should always be mindful of the risks associated with their equipment, as well as how they control their buoyancy.