Reverse Block and Scuba Diving

How Should You React If You Have a Reverse Block When Scuba Diving?

A scuba diver signalling OK


James + Courtney Forte / Getty Images

I had enjoyed an almost stress-free first dive with an open water course student when he suddenly flashed me the dreaded "not okay" sign during the ascent. Divers are trained to communicate a problem by signaling their dive buddy or guide with a flat hand turned side to side (like a so-so gesture). The most common situation in which I see a diver make this hand signal is in the case of ear equalization problems, and this was the case with my student. Before I could stop him, he pinched his nose shut and blew out his nose, as if he were equalizing his ears during a descent. Depending upon the reason for ear discomfort on an ascent, this may be the worst thing that a diver can do.

Why would a diver's ears hurt as he ascends? There are two obvious reasons. The first is common with new, inexperienced drivers who have not completely mastered their ascent techniques. Although the diver is attempting to ascend, he loses track of his depth and inadvertently descends without equalizing his ears. The second possibility is that the diver is experiencing a reverse block.

As an instructor, it is sometimes difficult to ascertain the reason for ear discomfort on ascent. An informed diver, however, can usually determine what is happening in his own body better than a dive guide can.

Ear Pain From Accidental Descent

As a diver ascends, the water pressure decreases causing the air trapped in his ears to expand according to Boyle's Law. Normally, the expanding air escapes from a diver's ears without the diver manually equalizing them - the diver's ears automatically equalize to the lower pressure. If the diver descends again, he will need to re-equalize his ears to compensate for increased pressure just as he did on on the original descent. Otherwise he will feel discomfort in his ears.
Once a diver understands that his ears need to be equalized each time he descends, he can learn to recognize how his ears feel with a slight increase of water pressure. This allows a diver to use his ears as a gauge to alert him if he begins to inadvertently descend while attempting to swim up. Other ways a diver can avoid an accidental descent is by vigilantly monitoring his depth gauge during his ascent and by using an ascent line as a visual depth reference.

Ear Pain From a Reverse Block

The other possible cause of pain on ascent is a reverse block. During ascent, air inside a diver's body air spaces exands. A reverse block occurs when exanding air is trapped inside a diver's ears. The trapped air exerts pressure and can mimic the pain of a skipped equalization during descent. However, the problem is the exact opposite. The pain of a reverse block on ascent is caused by too much air in the ears rather than too little. Most divers instinctively attempt a standard equalization by pinching their noses and blowing the moment they feel discomfort in their ears. In the case of a reverse block, this is the worst thing a diver can do, because it adds air to the already over-full ears and exacerbates the problem
In the case of a reverse block, a diver must descend to a depth where he experiences no pain in his ears, and then slowly ascend, allowing time for the trapped air in his over-full ears to escape. This can take minutes or longer, or sometimes not occur at all. In a worst case scenario, a diver with reverse block will eventually have to ascend as his air supply runs to zero, risking an ear barotrauma.

Reverse blocks are most common when sick divers ignore safe diving guidelines and use decongestants or other medicines to aid in equalization on descents. Underwater, drugs are metabolized more quickly than normal because of the high water pressure. A diver who uses medicine to equalize on descent may find that the medicine has worn off and is no longer effective at the end of the dive. Without the drugs to help his ears equalize as he ascends, the expanding air becomes trapped in the ears and causes pain.  Reverse blocks may also be caused by ear infections, which can often be prevented with ear beer.

How does a diver tell if he has a reverse block or has simply descended when he intended to ascend? The answer is tricky. The best thing a diver can do to avoid ear problems on ascent is to only dive when he is healthy and refrain from using drugs to help with equalization. Furthermore, a new diver should concentrate on learning proper buoyancy and ascent procedures such as monitoring his depth gauge on the ascent. In a worst case a scenario, a diver can either ascend or descend slightly and see which direction helps to relieve the pain. If ascending relieves the pain, he has simply descended inadvertently and should re-equalize his ears and continue his ascent, but if ascending increases the pain it is likely that he has a reverse block and must avoid adding more air to his ears and allow time for the air to work its way out. Learning to recognize the difference between an omitted equalization and a reverse block will keep divers comfortable and safe during an ascent.