How to Deploy a DSMB Safely?

What risks are there?

As you approach the end of your dive, often a DSMB will be deployed to the surface for a number of reasons:

To inform your dive boat of your location

To mark a certain area

To inform overhead water traffic that divers are below

Divers on a safety stop, about to surface.

There are a number of other reasons that you would deploy a DSMB (Delayed Surface Marker Buoy), above are just some, which relate to recreational divers and their activities.

The ‘DSMB’ (Delayed Surface Marker Buoy)

It is a key piece of dive gear and is an extremely useful tool when deployed correctly. However, if used incorrectly, it can put the user and others at high risk. In your PADI Open Water Course, you will learn how to do this skill, and your Instructor should make sure you master this skill well. This piece of equipment can be hazardous if it is not deployed correctly, improper use can result in a diver being dragged to the surface. Some DSMB’s are open-ended and can be inflated using your primary second stage, some have to be orally inflated.

Check and take care of your equipment.

After each dive check that your DSMB is rolled or folded in the correct way. Check that your finger spool or reel is correctly spooled. If not, remove any tangles or knots and rewind it. A badly spooled reel may cause a reel jam, or the line may snag or spring from the spool. Do not over-fill spools with too much line. This may cause entanglement when you try to deploy the line to the surface.

Choose the correct depth first.

If you are a beginner at this task, practice in shallow water or in a pool first until you are comfortable with the skill.

When you come to the end of your dive, ascend slowly to a depth of around 8 – 10 meters. Do not try to deploy your DSMB at a depth of 5 meters whilst doing your safety stop. If your deployment skills are not great, you will more than likely end up at the surface with your DSMB without doing a safety stop! Your buoyancy skills should also be well rehearsed, this makes the actual skill much easier.

Look up if all is clear?

Once at the correct depth, check above that all is clear. Make sure you are not going to deploy your DSMB into the middle of a group of divers. Check that there are NO other DSMB reel lines which cross the path of your intended deployment direction. Overhangs and overhead rocky environments are not ideal to deploy a DSMB. Move into a space that is free from boat propellers, you will not be popular with your skipper if his propeller becomes tangled in your reel line!

Never attach the reel to yourself.

Remove both the DSMB and reel from your pocket, BCD clip or where-ever you keep it. Never attach the reel to your BCD, wrist or any other part of your body. If a boat or jet-ski passes overhead and becomes entangled in your reel line, you will be dragged behind the watercraft and cannot free yourself. You should, at all costs be able to release the spool/reel and DSMB completely at any time for your own safety.

Buoyancy control.

When you are ready to deploy the DSMB, make yourself neural or slightly negatively buoyant. If you use oral inflation to deploy your DSMB, it is better to stay neutrally buoyant. Through your exhalation, you will slightly sink until you replace and breath from your regulator. If you deploy with an alternate air source (AAS) it is better to be slightly negatively buoyant. Be aware of any upward drag from the DSMB if you are slow to release it. Your buoyancy adjustments, whilst doing this skill can be controlled by deeper exhalation.

Clear the reel line from your body and gear.

When you are ready to inflate the DSMB, make sure the reel line is held away from your equipment. Fin-straps are notorious for entanglement. A BCD inflater or integrated weight quick releases are also a common place to snag your reel line on. This can lead to a hazardous situation and the DSMB could drag you to the surface.

How much air to put in?

It is easier at depth (8-10 m) to put air in the tube, rather than at 5 meters. At depth, you require less air inside as it expands when it travels upwards. If you put too much air in, the DSMB will rocket to the surface very quickly, and it expands as it goes. Sometimes, cheap DSMB’s that are glued, rather than stitched will tear open if too much air is inside. Fill the DSMB with small, short bursts, this will enable you to control it better. When the DSMB hits the surface, you can pull down slightly on the reel line to make the DSMB stand up at the surface. Slowly reel in the excess line and ascend to the required safety stop depth.

Alternate air source inflation.

Often this is the easier method for novice divers and beginners. If you use an alternate air source to inflate your DSMB, do not stick the AAS completely inside the DSMB neck. Hold the AAS under the open neck of the DSMB and give short bursts of air to inflate it. Be aware, your AAS and your hand are very close to the loop that is attached to the reel line. This is a primary concern for entanglements, so heightened awareness is required here.

Oral Inflation.

This method requires a little practice. Keep your primary regulator in your hand after you remove it from your mouth. Exhale into the DSMB then replace your regulator so you can breathe. Repeat this process two or three times until the DSMB has enough air inside.


Make sure your reels locking mechanism is in the open position, otherwise the DSMB will drag you up. Once the DSMB has hit the surface, slowly reel in any slack line and ascend to the required depth. Do not drop the reel, otherwise, it will unwind to the end. This would lead to chaos and meters of a floating line which will lead to entanglement.

Choose the right DSMB.

If you choose a large DSMB, it will take more air to deploy it. Bigger is not always better. If there is, not sufficient air inside the DSMB, it will not stand at the surface but will fall over and be floppy.

Practice makes perfect here. If you struggle with this skill, practice it in shallow water and, on open water dives with someone who can do this skill. A good way to improve this skill is to join our PADI Distinctive Specialty Surface Marker Buoy Course.

Safe diving to you all.

Dive Smart Gozo