DSMB stands for Delayed Surface Marker Buoy and it’s the acronym for the colourful, inflatable tubes used to mark a diver’s location. They roll up small so that you can enjoy your dive unhindered by a buoy line and then deploy them later to let boats and divers know that you are making your ascent.

DSMB’s are an essential part of a diver’s safety kit, particularly in poor visibility and/or strong current. For example, if you get separated from your party and have to do an emergency ascent alone, deploying your DSMB can save your life by making it possible for boats in the vicinity to find you, as well as avoid running over you.

Given that it’s a simple, inflatable tube you’d think that using a DSMB would be a piece of cake, but as with any bit of kit, things can go wrong.

The most common DSMB underwater deployment pitfalls I have observed are

  • entanglement – either with the inflatable tube itself (usually temporarily inconvenient rather than dangerous) or with the attached line (dangerous, as nylon lines can cause a range of injuries from superficial to life-threatening)
  • reel-jamming – potentially very dangerous as your DSMB can then tow you upwards at an astonishing speed, risking lung injury or decompression illness

Steps to Deploy your DSMB Safely

  1. Start at depth. It’s easier to control your buoyancy at depth, and you don’t have to put as much air into the DSMB – remember, any air you put into it will expand as you ascend.
  2. Make sure you are neutrally buoyant and that your buddies are well clear.
  3. Detach your DSMB reel from your BCD and make sure that the line is attached to the DSMB and runs freely.
  4. Unroll your DSMB tube and make sure it is smooth enough to begin inflating. Keep a firm grip on your reel while making sure your fingers and thumbs are in no danger of getting caught in the line or the winding mechanism (if your reel has one).
  5. Add air to your DSMB either by purging your octo or by holding the opening to catch your exhaust bubbles.
  6. Holding the reel and not the line, release your DSMB and let it the reel unspool as the DSMB starts to ascend.
  7. Make your way to the surface  at a safe rate, reeling in the line as you go to keep it taught to hold the DSMB is vertical at the surface.
  8. Don’t forget your safety stop!

Here is a useful video to watch: