Diver Question: Recently I’ve seen many reports of downdraft currents on various online forums accompanied by debates about the best method for escaping them. Do any of DAN’s experts have an opinion or advice?
As you will probably appreciate, there is no formal body of research addressing this specific question. The appropriate response and the degree of vigour required will be influenced by the depth, strength and volume of the downdraft, the distance from the eddy line (the edge of the draft), the topography, visibility, risk of entanglement or entrapment, the bulk of the diving equipment worn, the strength, power, buoyancy control, skill, decompression status (or obligation) of the diver and potentially other factors. What seems like a simple question quickly becomes impractical to study in a safe, controlled and still meaningful manner.
Even without quantification of the actual effort required, the question can be addressed conceptually. The priority is maintaining control — particularly vertical control — to avoid serious buoyancy and/or gas-space issues that could make the situation worse. Getting negative, hugging the reef and climbing out rock by rock might be workable if the strength and size of the current flow required it and the topography allowed it. The advantage of this approach is control. The diver is unlikely to have serious shifts in buoyancy or of gas in sensitive spaces (primarily the middle ears and lungs) when control is maintained.
Again, depending on the conditions, swimming perpendicular to the flow could be effective. An advantage of this may be a reasonable degree of control, with minimal need for fast changes in buoyant state or risk to sensitive gas spaces. Choosing to increase buoyancy probably represents the greatest risk of all. While it may be necessary in extreme situations, it is also possible that it could result in an overcorrection and the subsequent hazards of an uncontrolled ascent, the latter resulting in an elevated risk of barotrauma and decompression illness.
My fundamental recommendation is that divers think in advance and be prepared with a continuum of responses from which to choose and, when appropriate, to shift between. The progression of the graded response would be as follows: a mild downdraft could be ignored; a little more strength would prompt horizontal swimming to move out of the affected zone (with minimal or no addition of air to the BCD); even more strength or an uncomfortably large downdraft flow zone would prompt grabbing the wall for stability and, possibly, climbing out. A minor amount of gas might be added to the BCD at the hanging-onto-the-wall point, but not as a primary part of the solution. Adding too much positive buoyancy could create a situation more dangerous than the initial hazard. It could pull the diver off the wall, precipitate a runaway ascent or make what could otherwise be a mild case of entanglement extremely problematic.
Mental practice is an important way to improve skills and responsiveness. A critical part of this effort is to remember that every event has its own idiosyncrasies. Having multiple options and the physical skills and calm demeanour to employ them in a thoughtful, progressive manner will provide the best protection.
Answer provided by Neal W. Pollock, Ph.D.