28 days in saturation: what the month is actually like

The 28 days is a ceiling, not a plan

The number everyone repeats comes from two places, and both of them are limits rather than schedules.

The first is the UK Health and Safety Executive's Approved Code of Practice for offshore commercial diving, L103. Paragraph 83 says a diver should not remain in saturation for more than 28 days at a stretch, and that the 28 days includes decompression. Paragraph 84 adds that each saturation should be followed by a surface interval of the same length, and that anything shorter needs the diving contractor's hyperbaric medical adviser to be consulted first.

The second is DMAC 21, the Diving Medical Advisory Committee's guidance on how long a human being should be kept under pressure. It is written for places with no national rules of their own, and it is stricter than most people assume. Twenty-eight days is the normal maximum. An extension is possible only in exceptional cases, and only with written agreement from the contractor's medical adviser, the divers themselves and the supervisors. Over a year, no diver should accumulate more than 182 days of saturation exposure.

So the first honest thing to say about a 28-day saturation is that most saturations are not 28 days. Imbert and colleagues questioned 51 certified commercial saturation divers working from the DSV Deep Arctic in the Norwegian and UK sectors in 2015 and 2016. The mean saturation in that sample was 19.7 days, with a standard deviation of 6.5. Divers with a mean of 15.9 years of saturation experience were, on average, doing three-week saturations, not four-week ones.

The second honest thing is that the 28 days are not 28 working days. Decompression is inside the ceiling, and decompression from these depths is measured in days. In the same study, divers stored at 110 metres in the Norwegian sector decompressed over 5 days 4 hours; divers stored at 136 metres in the UK sector took 5 days 13 hours. Add the compression at the start and a theoretical 28-day saturation leaves you around 22 days in which bell runs can happen.

Sources: HSE, Commercial diving projects offshore (L103), second edition 2014; DMAC 21 Rev 2, June 2006; Imbert, Balestra, Kiboub, Loennechen and Eftedal, Frontiers in Psychology, published 11 January 2019.

Before the door shuts

Nothing about the month begins with the chamber. It begins with paperwork and a nurse.

You need a current certificate of medical fitness to dive from an HSE Approved Medical Examiner of Divers, valid for up to 12 months, and L103 extends that requirement to anyone whose job routinely puts them under pressure — which includes life support technicians, not just divers. The examination itself is set out in HSE's MA1 guidance, revision 5 of which was published in June 2023 and covers the respiratory, cardiovascular, neurological, ENT and mental health assessments an examiner should make.

On top of the annual certificate there is a second check that most write-ups of saturation life miss entirely. Paragraph 191 of L103 requires a medical check within the previous 24 hours, carried out by a nurse, a doctor or a diver medic, before any saturation exposure. DMAC 26 says what that check is partly looking for: cuts, wounds and abrasions, which may be photographed and reviewed with the diving medical adviser before you are allowed to spend a month in a warm, humid, sealed environment where Pseudomonas aeruginosa is the normal cause of superficial infection.

The team around you is also specified rather than improvised. L103 paragraph 95 sets a minimum of nine people for a closed bell dive, and paragraph 163 says that where saturation runs continuously there should be two supervisors on each shift. Paragraph 106 requires at least one life support person at the control point at all times, with another close by, and paragraph 107 requires a dedicated life support supervisor when life support control sits away from diving control. Paragraph 122 requires at least one diver medic in the team who is neither the supervisor nor the diver in the water.

Source: HSE, Commercial diving projects offshore (L103), para 95, second edition 2014. Two of the on-shift team must be competent to supervise; the relief supervisor may take breaks of about 30 minutes agreed with the supervisor (para 96).

None of this is improvised on the day. By the time the door shuts, every person on that list has a certificate with a date on it, and the 24-hour check has already been signed.

Day 0: blowdown

Blowdown is the part that sounds dramatic and is mostly uncomfortable.

Helium and oxygen are fed into the chamber until the internal pressure matches the storage depth. The rate in the Imbert study was 1 metre per minute. Kiboub and colleagues, working with 20 professional saturation divers off Stavanger in June and July 2015, recorded compression to a storage depth of 100 to 115 metres taking about two hours. At a metre a minute, a 136-metre storage depth is a little over two hours of continuous pressure change.

Three things happen in those two hours. Your ears have to be cleared continuously, because the pressure outside them is climbing the whole time. The chamber gets hot, because compressing a gas heats it, and the life support technician has to take that heat away. And your voice changes, permanently for the duration, because helium is far less dense than nitrogen and the resonant frequencies of your vocal tract shift upwards. That is not a novelty. DMAC 28, the current guidance on emergency medical care for divers in saturation, treats heliox speech as a clinical hazard: it notes that distorted speech relayed through intermediaries can lead to omissions and misinterpretation, and says an unscrambler should be considered. If a doctor on the surface cannot reliably understand a sick diver, that is a patient safety problem, not a joke.

The gas you are breathing also stops being air in a measurable way. Imbert's team recorded chamber oxygen partial pressure during compression at 21 to 45 kPa, settling to 38 to 42 kPa at storage depth. Kiboub's group recorded 40 kPa. In old money, that is around 0.4 bar of oxygen — roughly double the 0.21 bar you breathe on deck, held constant for weeks. Everything else in the mix is helium.

The box you live in

The living chamber is a pressure vessel with bunks in it. It is useful to know the actual dimensions, because they are smaller than most illustrations suggest.

DMAC 28 sets a minimum internal diameter of 1.8 metres for a chamber in which a casualty might have to be treated, and says more than 2.15 metres is preferable. Drass, one of the manufacturers that publishes specifications, gives an internal diameter of 2,300 mm for its saturation chambers and a 300-metre depth rating. That is the inside of a cylinder a little over two metres across, which has to contain bunks, a toilet, a shower and the people using them.

The medical lock — the small pressure lock through which anything hard has to pass — is specified at a minimum of 300 mm in diameter by DMAC 28. Everything you receive for a month, from food to a replacement toothbrush to drugs, goes through a hole about the width of a dinner plate.

Environmental control is a plant item rather than a thermostat. Drass lists environmental control units with more than 18 kW of heating and more than 18 kW of cooling, each covering chamber volumes totalling over 30 cubic metres, plus a sanitary water system delivering more than 80 litres a minute so that more than one shower can run at once, and a 1,000-litre reserve boiler heated to a maximum of 58 °C.

Two structural details from L103 shape daily life more than any of this. Paragraph 72 says the internal doors between chambers should be kept closed except when someone is passing through, so the complex is a sequence of sealed compartments rather than an open corridor. And paragraph 141 requires the bell itself to be able to sustain trapped divers for at least 24 hours — which is the reason the bell is cramped with survival equipment as well as diving equipment. Our post on what the closed bell is and how it works goes through that fit-out; life inside the saturation chamber covers the living space in more detail.

If you want a sense of how many of these spaces exist at all, our own count of the saturation fleet found 493 diver berths across 28 vessels — the entire global capacity for living under pressure at sea, at any one moment, is a few hundred bunks.

How the 24 hours divide

This is where the day-by-day accounts on the internet usually go wrong, because they describe a shift pattern without reference to the rules that constrain it.

The hard numbers are in L103 paragraphs 97 and 98, and in HSE Diving Information Sheet No 7, which exists specifically to define bell run and lock-out times. A bell run is measured from the moment the clamp is first removed — lock-off — until it is reconnected ready for equalisation. Eight hours is the maximum, and returning the bell to the system part-way through does not restart the clock or allow the run to extend beyond eight hours from the original lock-off.

Within that eight hours, how long you personally spend wet depends on how many of you are in the bell. In a two-man bell, each diver gets up to four hours in the water. In a three-man bell, two lock out together while the third stays dry as bellman, and each diver may accumulate up to six hours in the water provided a refreshment break is taken within four hours of the start of lock-out — DVIS 7 puts a floor of 15 minutes on that break. If all three have to lock out, each lock-out drops back to four hours.

Then there are the rules about what you cannot do. No diver should take part in more than one six-hour lock-out or one eight-hour bell run in a pre-planned 24-hour period. Every diver in saturation must have at least 12 continuous hours of rest in each 24, and DVIS 7 is explicit that the rest period excludes diving and the checks either side of it. HSE also names and rejects a specific practice: "ratcheting", in which the whole team is cycled through in under 24 hours and the cycle then immediately restarts.

Sources: HSE Diving Information Sheet No 7 (rev 1), Bell run and bell lock out times, published January 2018; HSE L103 paras 97–98, 2014; DMAC 20 Rev 1, November 1997.

Put those together and the shape of the 24 hours is fixed before anyone writes a roster. An eight-hour bell run and a 12-hour rest period already account for 20 hours, and the remaining four are absorbed by handovers, meals, pre-dive checks and the time the bell takes to get down and back. On a vessel running saturation continuously, divers in the same chamber are typically on different shifts, which is why the living chamber is rarely all asleep or all awake at once. That pattern is custom, not regulation — the only shift rule in L103 is paragraph 163's requirement for two supervisors per shift.

The bell run, lock-off to lock-on

The bell is the working day. You climb into it from the chamber complex at storage pressure, the clamp comes off, and the bell is lowered to the worksite.

The depth you work at is not the depth you live at. In the Imbert sample, Norwegian-sector divers stored at 110 metres worked at 121 metres and UK-sector divers stored at 136 metres worked at 155 metres. Kiboub's group, stored at 100 to 115 metres, had a maximum working depth of 125 metres. The excursion from storage depth to worksite is a real decompression consideration, which is why DMAC 31 draws a line between divers who have made an excursion in the previous 24 hours and those who have not when it discusses how fast an emergency decompression can safely go.

Breathing gas oxygen goes up for the dive. Imbert recorded 60 to 80 kPa during excursions; Kiboub recorded 60 kPa. L103 paragraph 43 gives 1.4 bar as the recommended maximum oxygen partial pressure, and DMAC 04 applies the same 1.4 bar ceiling to the gas in the open-circuit bail-out bottle, with a floor of at least the partial pressure of the primary mix and never less than 0.4 bar. DMAC's reasoning is worth knowing: the committee judged that the benefit of a richer bail-out mix is small, because saturation excursions are short, while a seizure during a bail-out could be fatal.

Cold is the other governing problem, and it is a physics problem rather than a comfort problem. Kiboub's divers worked in water at 4 °C. L103 paragraph 81 requires active heating for oxy-helium divers and, beyond 150 metres, heating of the breathing gas itself; DMAC 20 puts the threshold at about 150 metres too. DMAC's 1981 thermal stress workshop quantified why: respiratory heat loss at 80 metres over an hour was put at roughly 200 W, which the group considered unacceptable without a heat exchanger, and because helium carries heat away so much faster than air, the maximum tolerable inspired gas temperature is lower — around 40 °C rather than the 45 °C that would be uncomfortable in humidified air at the surface.

Fluid loss is the limit nobody expects. DMAC 20 records measured losses of up to 5% of body weight after four hours of heliox breathing with active heating, and recommends that divers be offered the chance to return to the bell for fluid during any lock-out longer than two hours. It also says a diver should not eat a heavy meal within two hours of a dive, and that returning to the bell to eat or drink should not be discouraged. DMAC 20's conclusion, after all of that, is that no fixed physiological limit on lock-out length exists: fatigue is the controlling factor, the diver and the supervisor should set the length between them, and the diver must keep enough strength in reserve to rescue himself or a colleague.

Food, water and keeping clean for a month

This is the half of the month that no published code quantifies and every diver remembers.

Food comes through the service lock, hot, in sealed pots, and it arrives on the shift's schedule rather than the galley's. There is no published calorie figure for a saturation diver in any of the codes of practice — if you see one online, ask where it came from. What the guidance does cover is hygiene. DMAC 26 requires HACCP food safety management, says unused food and drink should be locked out promptly, and bans the sharing of drinking cups. It also bans travel bags from the chamber: a brand-new bag should be used for the living quarters, and the number of pouches, clothes and personal items inside should be kept down.

Water is a managed hazard. DMAC 26 asks for potable water samples tested at regular intervals through an accredited laboratory, testing for Legionella where water has come from bunkered onshore supplies, point-of-use medical-grade filters on showers and taps, and particular care on vessels that have been idle for weeks. It notes that Legionella thrives between 20 °C and 45 °C in man-made water systems — which describes a saturation chamber's shower circuit rather well.

Personal hygiene is near-clinical. DMAC 26 recommends a shower at least once a day and after every bell run, with a neutral or slightly acidic soap; drying the head and neck first, ideally with a separate towel; keeping the ear canal occluded while showering, for instance with gauze and petroleum jelly; nails cut straight across; teeth brushed at least twice a day; no sharing of razors, toothbrushes, combs or towels. Prophylactic acetic acid drops may be used, three to four per ear, held for a timed minute, twice a day and after each dive or shower, with each diver keeping two labelled bottles, one per ear. The guidance is firm that prophylactic drops will not treat an established infection and that treatment drops must not be used as prophylaxis.

Cleaning is a rota. Daily: the toilet, sink and shower areas, the service locks and table surfaces. Twice weekly: chamber walls, bulkheads, built-in breathing system masks, and shower heads removed and cleaned outside. Disinfectant is applied by cloth or sponge — never aerosol — left in contact for at least ten minutes, then rinsed and dried, working from the top of the chamber down. Laundry, including pillowcases, goes at a minimum of 85 °C, and cleaning water should be at least 60 °C.

Humidity is the one environmental figure people most want and the guidance most conspicuously declines to give. DMAC 26 says only to keep humidity at the dry end of the comfort range. DMAC 19, from 1990, takes the position that a higher water vapour content in the breathing mixture is not harmful and is good for the respiratory tract. Neither document names a percentage. DMAC 26 does say plainly that infection risk rises with the length of the saturation, and recommends bringing the chamber to surface periodically for a thorough clean and dry — which, on a long campaign, is a scheduling decision rather than a hygiene one.

Sleep, noise and what the month does to your head

You get 12 continuous hours of rest in every 24 by law. Whether you sleep through them is another matter, and here the published evidence is thinner than the topic deserves.

What is documented is the noise. HSE's Diving Information Sheet No 14 applies the standard noise exposure action values to divers — 80 dB(A) lower, 85 dB(A) upper, 87 dB(A) limit, with peak values of 135, 137 and 140 dB(C) — and states that compression chambers can be noisy, particularly older designs built without noise-reducing features. It also makes a point that matters for anyone told the problem is managed: limiting dive time alone is not an acceptable way to control noise exposure. What DVIS 14 does not do is publish a measured decibel figure for the inside of a saturation living chamber. As far as we can find, no public source does. The environmental control unit, the gas flow and the scrubber run continuously, and the number is not in the literature.

On the psychological side, the Imbert questionnaire is the most useful published data because it asked the divers themselves rather than describing them. On a one-to-ten scale, the 51 divers rated their general well-being at 6.18 ± 1.56 and their alertness at 6.23 ± 1.91. Mid-range scores from experienced professionals — the mean age was 46.1 and the mean saturation experience 15.9 years — are not a complaint, but they are not a glowing account of the environment either.

DMAC 32, which exists for the worst case, makes a related observation in passing that no brochure will: keeping a deceased colleague in the living area is a significant psychological stress on the divers who remain, some of whom may have to continue working for the sake of the investigation.

The gas you breathe for 28 days

Saturation is, more than anything else, a month of breathing a controlled mixture. Here is what the numbers actually are, from the two published studies that reported them.

Sources: Imbert et al., Frontiers in Psychology, 11 January 2019; Kiboub et al., Frontiers in Physiology, 16 July 2018; HSE L103, 2014; DMAC 04 Rev 2, May 2016.

Oxygen at roughly twice its surface partial pressure for weeks is not a neutral exposure. Kiboub's team found broad downregulation of genes governing haem, haemoglobin and erythrocyte function after saturation, which they read as acclimatisation to hyperoxia, alongside upregulated antioxidant genes. Haematocrit fell measurably across the saturation: from 41% to 39% in the group taking vitamins C and E, and from 40% to 38% in the controls. Supplementing with those vitamins made no difference to the gene expression profiles or the plasma biomarkers.

Gas purity is a separate discipline. HSE's Diving Information Sheet No 9 applies BS EN 12021:2014, which caps carbon dioxide in breathing gas at 500 parts per million, carbon monoxide at 5 ppm and oil at 0.5 mg per cubic metre, with no liquid water present. Where gas comes from a compressor system — including a reclaim compressor, unless the manufacturer certifies it oil-free — the sheet says testing should happen at least every three months. Reclaim matters on a sat vessel because helium is expensive and gets recycled; L103 paragraph 130 requires a carbon dioxide analyser with an alarm wherever gas reclaim plant is in use.

Decompression: the slowest week of the campaign

You do not come up at the end of a saturation. You are brought up, slowly, with the chamber as it is, while you continue to live in it.

The measured durations from the Imbert study are the best public figures we have found for what this takes in the North Sea:

Durations from Imbert et al., Frontiers in Psychology, 11 January 2019, and Kiboub et al., Frontiers in Physiology, 16 July 2018. The implied rates are our own arithmetic on the published total elapsed durations; neither study states whether pressure travel is continuous or interrupted, so the instantaneous rate during travel may be higher than the average.

Oxygen is raised for the ascent — to 46 to 50 kPa in the Norwegian sector and 48 to 52 kPa in the UK sector — because a higher oxygen partial pressure widens the gradient that drives helium out of the tissues. By the time the chamber is near the surface, the atmosphere is back to something close to air at 21 to 23% oxygen.

How fast could it go if it had to? DMAC 31, written after a 2013 workshop on accelerated emergency decompression, is the only public document that answers directly. Its position is that decompression should be as slow as the emergency allows; that about 10 to 20 metres per hour may be achievable with a high oxygen partial pressure, but only for divers who have made no excursion in the previous 24 hours; that chamber oxygen may be pushed to 1.0 to 1.5 atmospheres at deeper depths, requiring a built-in breathing system; and that up to roughly a litre of fluid an hour by mouth may be reasonable over a short decompression. Those are emergency figures. Comparing them with the five-and-a-half days above tells you how much margin a normal decompression carries. The emergency case is covered in more depth in our post on hyperbaric rescue and evacuation from saturation.

The first hour out, and the week after

The door opens at surface pressure and you walk out into a corridor on a ship. What happens next is the best-documented part of the whole month, because somebody asked the divers.

Source: Imbert, Balestra, Kiboub, Loennechen and Eftedal, Commercial Divers' Subjective Evaluation of Saturation, Frontiers in Psychology, published 11 January 2019. Denominators differ because not every diver answered every question; percentages are as reported in the paper.

Two things stand out. The first is that recovery is not instant: the mean was more than four days, and one diver in the sample reported ten. Recovery time showed no correlation with age. The second is that no venous bubbles were found, which the authors read together with the headaches and pallor as pointing to oxygen acclimatisation rather than subclinical decompression sickness — and they described the effects as reversible after decompression.

You also cannot simply get on a helicopter. DMAC 07 sets minimum surface intervals before flying, assuming a cabin altitude of 2,000 feet for a checked offshore helicopter flight and 8,000 feet for everything else.

Source: DMAC 07 Rev 2, Flying after diving, November 2017. These are minima, and DMAC recommends longer intervals where a journey involves several take-offs. DMAC 07 carries a separate row for heliox saturation that we could not read reliably in the copy we fetched, so check the source itself for that figure rather than assuming it matches the row above.

When it goes wrong, up to and including the worst case

A saturation system is built around the assumption that the people inside it cannot be taken out quickly. Every emergency provision follows from that.

L103 paragraph 74 says a seriously ill or injured diver in a chamber should be treated inside the chamber and not moved until stable. DMAC 28 spells out what that means in practice, and is unusually candid about the limits: few medical devices are built for hyperbaric use, so electrical equipment needs a documented risk analysis; simple manual aspirators are insufficient for acute airway suction; and the specialist knowledge required is rarely available under contract on site. Its stated approach is to stabilise the patient inside and then bring the vessel to port, where definitive treatment happens at atmospheric pressure. It also asks for access to a treatment chamber within 30 to 60 minutes allowing for pressure changes, a duty diving doctor on call around the clock, a waist-high bunk that tilts to 30 degrees at either end, and saturation-rated telemedical monitoring for blood pressure, ECG, pulse, temperature and oxygen saturation.

If the ship itself has to be abandoned, L103 paragraph 68 requires hyperbaric evacuation arrangements that maintain life support for at least 72 hours, and paragraph 67 requires a contingency plan for recovering a lost bell. IMCA maintains dedicated guidance on lost bell survival (D 017) and, since January 2026, on preventing and mitigating lost bell emergencies (D 077). Paragraph 152 requires a two-person, two-compartment chamber at the worksite, which is the subject of our post on the deck decompression chamber. Paragraph 135 requires communications recordings to be kept until 48 hours after the diver returns to the surface or to the saturation living chamber — a detail that only makes sense once you understand that an investigation may start days before anyone involved can be interviewed at surface pressure.

And then there is the case nobody writes about. DMAC 32, issued in January 2014, is guidance on dealing with the body of a diver who dies in saturation. Its reasoning is worth stating plainly, because it explains something about saturation that no amount of description of bunks and food will. A body at depth is saturated with helium. Without circulation, that helium cannot be eliminated the way it is in a living diver, so gas forms in the tissues and can interfere with a post-mortem. Only extremely slow decompression, relying on diffusion alone, would avoid that — and slow decompression is not possible, because decomposition advances, and the warm heliox environment speeds it up.

The recommended procedure is therefore to notify the regulatory authority — in most countries the police, and in Scotland the Procurator Fiscal, who becomes responsible for the body — take no action without their approval, photograph the deceased before anything else, move the body to an isolatable part of the complex, bag it with absorbent material at all orifices, reduce the heating in that compartment, and decompress the body over three to four hours. Freezing is prohibited outright. The other divers, meanwhile, are still in the complex, days from the surface.

What the internet gets wrong about the 28 days

That 28 days is the standard length. It is the regulatory ceiling. The measured mean in the only published North Sea sample we found was 19.7 days, and the 28 days includes five or six days of decompression.

Monthly salary figures. Pay is the most confidently stated and least verifiable number in this field. In the UK the baseline is the Offshore Diving Industry Agreement, a collective agreement between five diving contractors and the RMT, whose current settlement runs to 31 December 2026. ODIA does not publish its rate schedule; the figures in circulation are third-party reproductions of the Schedule of Rates dated January 2026, and cannot be checked against the primary document. The documents ODIA does publish, such as the November 2014 Diver Competency Pay Grading Matrix, define grades and competence criteria without attaching a figure to them: to qualify as a Professional Bell Diver under that matrix a diver needs 100 closed bell lock-outs and 400 lock-out hours in the water. So when a page gives you a precise monthly saturation salary, it is not quoting the agreement itself. We take one of those reproductions apart in what a saturation diver actually earns, cover what can and cannot be established about pay in what commercial divers are paid, and what to look for in your own terms in what to check in a campaign contract before signing.

Saturation diver death rates. There is no published fatality rate specific to saturation divers, by year or otherwise. The closest industry-wide figure is IMCA's annual safety statistics: the 2025 report covers 167 contributing companies and 1,020,036,687 man-hours, records seven fatalities — four offshore, three onshore — and gives a Fatal Accident Rate of 0.69, a Lost Time Injury Frequency Rate of 0.27 and a Total Recordable Injury Rate of 0.98. That 0.69 is built on all seven deaths against all 1,020,036,687 hours, not on the four offshore ones; the report's offshore-only rate, four fatalities over 524,483,938 offshore hours, is 0.76. The report does not break any of that out by diving, let alone by saturation diving. Anyone quoting a saturation-specific annual death toll is either using a different dataset they should name, or inventing it.

"Last breath". The phrase comes from a dramatised account of a North Sea saturation diver who survived losing his gas supply on the seabed. The 2025 feature film Last Breath, directed by Alex Parkinson and released by Focus Features on 28 February 2025, is the version most people have seen; Chris Lemons, the diver concerned, describes himself as a saturation diver and speaker on his own website. We are not going to repeat the depth and the duration you will find quoted elsewhere, because neither the distributor's page nor his own site states them, and we could not get to a primary account of the incident.

Diving bell spiders. These queries land on saturation pages constantly, and they are about a different thing entirely. Argyroneta aquatica builds a silk dome underwater and stocks it with air carried down in the hairs on its body; according to Britannica, the inflated web then behaves like a gill, drawing dissolved oxygen out of the water, and the spider has to return to the surface roughly once a day to top it up. It eats aquatic invertebrates — water mites, water boatmen, phantom midge larvae — and hunts rather than trapping them. The analogy with a diving bell is real: both are a gas space held under water. The difference is that a saturation bell has an umbilical, and the spider does not.

Hyperbaric chamber treatment prices. A clinical hyperbaric oxygen chamber and a saturation system are different machines doing different jobs, and the price of a hospital treatment session tells you nothing about either. What is relevant offshore is that L103 requires a two-person, two-compartment chamber at the worksite, and that DMAC 28's specification for a chamber in which a casualty might be treated starts at 1.8 metres internal diameter.

Seattle. Commercial diving schools and jobs in Seattle come up often enough to be worth a straight answer. The Divers Institute of Technology is in Seattle and runs a seven-month commercial diver programme; its programme page does not say that closed bell or saturation diving is taught, and does not publish tuition. Our own count of 34 diving schools found only five teaching saturation anywhere in the world, which is the honest context for any search that pairs a city with the word "saturation" — the full list is in our school directory.

The costs of the month that nobody itemises

A 28-day saturation does not cost you 28 days. Working through the rules gives a longer figure, and it is the number that should shape how you think about the trade.

Start with the surface interval. DMAC 21 and L103 both say it should match the length of the saturation you have just completed, and a shorter one needs the contractor's hyperbaric medical adviser consulted. A 28-day saturation therefore implies 28 days before the next one — a 56-day cycle. Against the 182-day annual cap on saturation exposure, that caps you at six 28-day saturations in a calendar year, consuming 336 of the 365 days. That is an arithmetic ceiling derived from the guidance, not a roster anyone works; the point is that the guidance already forecloses the idea of being in saturation most of the year.

Then add the parts that sit outside both the saturation and the interval. A medical check within 24 hours before you are compressed, which means being on board and well before that clock starts. At the far end, a minimum of 24 hours on the ground before a 2,000-foot helicopter flight after saturation, 48 before anything else — minima that DMAC advises lengthening for journeys with several take-offs. And then a mean of 4.31 days to feel recovered, by the divers' own reckoning, with a reported range running to ten.

Deep work compresses the calendar further. DMAC 21 says that for saturations beyond 200 metres the surface interval should preferably be 28 days or more regardless of how long the saturation was. Given that our audit of the fleet found 17 of 22 depth-rated vessels sitting at exactly 300 metres, that is not a hypothetical band.

Two more costs are structural rather than personal. Saturation work exists only where somebody owns a system: our survey of 876 commercial diving companies found that just 17 of them run saturation, 1.9% of the industry. And the work has to be within reach — only 41% of the offshore platforms we catalogued sit inside a 300-metre water depth. Together those two facts explain why saturation campaigns are scheduled around vessels rather than around divers, and why the gap between saturation and surface-supplied work is as much about employment patterns as about technique.

None of this is a reason not to do the job. It is a reason to count the year rather than the month. If you want the long view of how this method came to be the normal way of working at depth, start with the history of saturation diving.

Sources

1. Health and Safety Executive — Commercial diving projects offshore: Diving at Work Regulations 1997, Approved Code of Practice (L103), second edition 2014, consulted 8 October 2026.
2. Health and Safety Executive — L103 publication page, consulted 8 October 2026.
3. Health and Safety Executive — Diving Information Sheet No 7 (rev 1): Bell run and bell lock out times, published January 2018, consulted 8 October 2026.
4. Health and Safety Executive — Diving Information Sheet No 9 (rev 2): Divers' breathing air standard and the frequency of tests, published January 2018, consulted 8 October 2026.
5. Health and Safety Executive — Diving Information Sheet No 14: The noise exposure of working divers, published March 2011, consulted 8 October 2026.
6. Health and Safety Executive — Diving publications and information sheets index, consulted 8 October 2026.
7. Health and Safety Executive — MA1 (rev 5): Medical examination and assessment of working divers, published 5 June 2023, consulted 8 October 2026.
8. Diving Medical Advisory Committee — Guidance notes index, consulted 8 October 2026.
9. DMAC 04 Rev 2 — Oxygen content in open circuit bail-out bottles for heliox saturation diving, May 2016, consulted 8 October 2026.
10. DMAC 07 Rev 2 — Flying after diving: recommendations, November 2017, consulted 8 October 2026.
11. DMAC 08 — Thermal stress in relation to diving (workshop report), March 1981, consulted 8 October 2026.
12. DMAC 19 Rev 1 — The effects of water vapour on diver physiology, November 1990, consulted 8 October 2026.
13. DMAC 20 Rev 1 — Duration of bell lockouts, November 1997, consulted 8 October 2026.
14. DMAC 21 Rev 2 — Guidance on the duration of saturation exposures and surface intervals between saturations, June 2006, consulted 8 October 2026.
15. DMAC 26 Rev 1 — Saturation diving chamber hygiene, January 2016, consulted 8 October 2026.
16. DMAC 28 Rev 3 — The provision of emergency medical care for divers in saturation, January 2024, consulted 8 October 2026.
17. DMAC 31 — Accelerated emergency decompression (AED) from saturation, March 2013, consulted 8 October 2026.
18. DMAC 32 — Guidance on dealing with the body of a deceased diver in saturation, January 2014, consulted 8 October 2026.
19. Imbert JP, Balestra C, Kiboub FZ, Loennechen Ø, Eftedal I — Commercial Divers' Subjective Evaluation of Saturation, Frontiers in Psychology 9, doi:10.3389/fpsyg.2018.02774, published 11 January 2019, consulted 8 October 2026.
20. Kiboub FZ, Møllerløkken A, Hjelde A, Flatberg A, Loennechen Ø, Eftedal I — Blood Gene Expression and Vascular Function Biomarkers in Professional Saturation Diving, Frontiers in Physiology 9, doi:10.3389/fphys.2018.00937, published 16 July 2018, consulted 8 October 2026.
21. IMCA — Annual Safety Statistics Report 2025, consulted 8 October 2026.
22. IMCA — Safety statistics, consulted 8 October 2026.
23. IMCA — Guidance document register, consulted 8 October 2026.
24. IMCA — Document catalogue, consulted 8 October 2026.
25. Offshore Diving Industry Agreement — home page, consulted 8 October 2026.
26. Offshore Diving Industry Agreement — work programme and agreement periods, consulted 8 October 2026.
27. Offshore Diving Industry Agreement — Diver Competency Pay Grading Matrix, Rev 01, November 2014, consulted 8 October 2026.
28. Drass — Saturation chambers specifications, consulted 8 October 2026.
29. Drass — Life support system specifications, consulted 8 October 2026.
30. Encyclopaedia Britannica — Water spider (Argyroneta aquatica), consulted 8 October 2026.
31. Focus Features — Last Breath (2025), directed by Alex Parkinson, consulted 8 October 2026.
32. Chris Lemons — official website, consulted 8 October 2026.
33. Divers Institute of Technology, Seattle — commercial diver programme, consulted 8 October 2026.

Frequently asked questions