How to Deploy an SMB (DSMB) From Depth, Step by Step

What is the difference between an SMB and a DSMB?

A DSMB (delayed surface marker buoy) is sent up from depth; an SMB, in the strict sense, is inflated at the surface or towed for the whole dive. DAN's definition turns on one part: a DSMB has an over-pressure valve that lets expanding gas escape on the way up, as Boyle's law predicts. An SMB without that valve should only be inflated at the surface, because sending it up from depth can damage it. As DAN puts it, a DSMB is technically an SMB, but an SMB is not a DSMB.

Usage is looser than the definitions. PADI uses SMB for the family and DSMB for a buoy used at the end of the dive, SSI describes the classic SMB as a round buoy inflated at the surface before the dive, and the tube-shaped buoy is often called a safety sausage. This guide covers sending one up from depth. Our safety stop guide explains why you would hold a stop under one in current. Other topics on being seen and staying safe are in our safety guides.

Open, self-sealing or closed: which design?

A closed buoy with an over-pressure valve is the most forgiving at the surface; an open-bottom one is the simplest to fill. The trade-off is what happens once the buoy is up. An open tube keeps its gas only while the line holds it upright, and a dive resort's buyer's guide notes that without steady downward tension it can fall over and collapse. A sealed buoy keeps its gas until you dump it or the valve vents, which is why it must have that valve.

How to inflate a DSMB: mouth, octopus or inflator hose

Any of them works with practice. DAN lists oral inflation, exhaling from your second stage, purging an octopus into the open bottom and attaching a low-pressure inflator hose from a BC or drysuit, and calls all of them viable with proper training and regular practice. The differences are in what they do to your buoyancy and your hands.

Cold water changes the choice. Scubapro's regulator manual follows EN 250 in treating water below 10 °C (50 °F) as cold, warns that high air flows cool the first stage rapidly, and advises against using the purge button unless absolutely necessary. A long purge from your octopus into a buoy is exactly that kind of flow, so in cold water the inflator hose or your own breath is the safer choice.

• Exhaust bubbles. PADI's method is to hold the buoy above your head and catch the bubbles from your regulator.
• Oral inflation. PADI's reminder: keep taking regular breaths between puffs. Instructor Mark Russell, writing in DIVE Magazine, points out the advantage: gas exhaled from your lungs into the buoy leaves the buoyancy of the whole system almost unchanged.
• Octopus purge. Russell holds the reel and one side of the opening in his left hand, keeps the mouth open with his right fingers and purges the octopus with his right thumb. It adds gas quickly, so dump a little BC air before you start.
• Low-pressure inflator. Disconnect the hose from your BC or drysuit and connect it to the buoy's inflation valve; closed buoys such as Halcyon's are built for an oral or LP hose connection. Practise reconnecting the hose to the BC afterwards.

How to deploy a DSMB from depth, step by step

Get stable first, then work slowly. PADI places deployment at the safety stop, before you ascend, while Russell prefers about 10 m when possible, because at that depth you are less affected by the change in buoyancy than at 5 m and have more time to react. PADI's DSMB course trains deployment both from a stationary position and in mid-water. The steps below combine PADI's sequence with DAN's safety rules.

• Before the dive, stow the buoy and spool where either hand can reach them, and put a cutting tool where you can get it without looking. DAN wants one within reach every time you deploy.
• At deployment depth, get neutral and stop moving. Signal your buddy, who should watch you and stay clear of the line.
• Look up and around. PADI's sequence starts with checking your surroundings for obstacles, and anything overhead matters most.
• Unroll the buoy, clip the line to it, release the reel's lock and let out a short length of line. Keep the line taut and away from your body, as DAN advises.
• Dump a little air from your BC and exhale as you fill the buoy. Russell's tip limits the upward pull at the moment of release.
• Fill the buoy and let go of it, holding only the reel or spool. Let the line run freely through your fingers or off the reel.
• If anything jams, open your hand. In DAN's words, never clip the reel or spool to yourself during deployment, because the buoy's lift can pull you into a rapid ascent.
• Once the buoy is up, lock the reel and take up the slack as you ascend so the buoy stays upright. SSI notes that the reel also gives your team a depth reference during the stop.

Reel or finger spool, and how much line?

A spool for most recreational diving, a reel if you dive in thick gloves. DAN's summary is that a reel is easier to deploy and a spool is more difficult to jam. Russell suggests a simple finger spool for warm water and a hand-held reel with a clutch in cold water, where gloves make a spool awkward.

The line has to be longer than your deployment depth. SSI's rule is enough line for the buoy to reach the surface. Russell treats 20 m as enough for shallow recreational diving, and GUE's standards call for a spool with at least 30 m (100 ft) of line. Keep the spool separate from the buoy: Russell advises against lines permanently attached to the buoy, because they tangle and limit how deep you can deploy.

Why DSMB deployments go wrong

Mostly through buoyancy and line handling. BSAC's safe diving guide calls DSMB deployment one of the most common things to go wrong on a dive, and its return-to-diving advice names buoyancy control and DSMB deployment as skills frequently implicated in incidents. BSAC also warns that a buoy clipped to you and caught by anything at the surface can take away your buoyancy control.

A diver's report published by DAN shows how fast it happens. A diver at 13 m (43 ft) was sending up a self-inflating DSMB when the reel's ratchet release lever broke and jammed the reel. Letting go would have solved it, but the broken spring hooked the diver's glove. The computer logged an ascent rate peaking at 72 m/min (236 ft/min) over 7 m (23 ft) before the diver tore free near 6 m, then dumped air and took the last 4 m slowly. On deck the crew asked about symptoms of decompression sickness and kept oxygen at hand. Our decompression sickness guide lists what to watch for after an ascent like that.

What do SMB colours mean?

There is no worldwide standard. DAN says orange and yellow are the most common colours and give the best visibility, but that no industry-standard colour exists.

The UK has a convention, and it is worth knowing if you dive there. BSAC writes that the general UK consensus is to deploy an orange or red buoy in normal conditions and a yellow one in an emergency or when help is needed, while adding that a yellow buoy does not always mean an emergency. Its safe diving guide describes a related signal: one buoy means all is well, and a red and a yellow buoy on the same line means a problem. BSAC suggests writing 'Emergency' and your name on a yellow buoy used this way.

Makers build for the same idea. Halcyon sells its closed buoys in yellow, pink and orange so that divers can carry one for position and another for an emergency. None of it works unless the boat knows the code, and BSAC's rule is to brief all divers and surface cover, skipper included, on what each colour means before the dive.

Practice drills for DSMB deployment

Start in a pool, with someone watching. DAN recommends practising in a pool with a buddy, getting an instructor's guidance, and then deploying a DSMB at the end of every dive, because repetition builds proficiency. BSAC's advice is to practise the skill regularly. The drills below follow what PADI's DSMB Diver course trains over its two dives. Good weighting makes all of them easier; our weighting guide covers the check.

• Stow and unstow. Take the buoy and spool out and put them away again while hovering, without looking down for more than a moment.
• Stationary deployment. Send the buoy up while hovering neutrally at a fixed depth, at first in a pool or shallow water with an instructor or buddy watching.
• Mid-water deployment. Deploy while holding depth with no bottom reference, the way you would on a drift or blue-water ascent.
• Swim with the buoy. Tow it while managing the reel and line, keeping the line taut.
• Safety stop on the line. Hold 3 minutes at 5 m using the line as your depth reference, then reel in as you surface.
• Jam drill. With an instructor, practise letting go of the reel the moment it stops paying out, and reaching your cutting tool with either hand.