Knowledge Hub
Diving knowledge, in one place
Reference only — not validated for dive planning. Decompression planning is disabled. Always follow your training, your company's procedures and the applicable regulations.
Dive flags & signalsDiver-down and Alpha flags, hand and line signals.Emergency guidanceEmergency numbers, Channel 16, MAYDAY script and first steps.
General
Pre-dive checklist
- Confirm the dive plan, objectives, maximum depth and time, and abort criteria with everyone involved.
- Check fitness to dive: valid medical, feeling well, rested, no alcohol, no recent illness or congestion.
- Inspect and function-test all life-support equipment: regulators, gauges, computer, cylinders, valves, BCD/harness, hoses.
- Analyse every breathing gas yourself and label the cylinder (see the gas analysis guide).
- Agree hand/rope/voice signals and lost-communication procedures before entering the water.
- Check the site: weather, current, visibility, boat traffic, overhead or entrapment hazards, permits and isolations.
- Know where the emergency equipment is: oxygen kit, first-aid kit, radio/phone, and the nearest chamber and medical facility.
- Commercial work: complete the job safety analysis/toolbox talk and use the company checklist — it takes priority over this list.
Sources: IMCA — International Marine Contractors Association · ADCI — Association of Diving Contractors International · NOAA Diving Program
Commercial
Emergency procedures & lost communications
- Every operation must have a written emergency and contingency plan, rehearsed before diving starts.
- Lost communications: follow the pre-agreed procedure (typically rope-pull signals, then terminate the dive and return to the stage/bell or ascend as briefed).
- On loss of main gas supply the diver goes to bailout, informs the surface if possible and aborts the dive.
- The standby diver must be dressed in, briefed and ready to enter the water immediately.
- Keep the emergency contact list (chamber, medical advisor, coastguard, client) posted at the control position.
- After any incident: make the diver safe, give first aid/oxygen, get medical advice, then preserve records and report as required.
Sources: IMCA — International Marine Contractors Association · UK HSE — Diving at Work · OSHA — Commercial Diving Operations (29 CFR 1910 Subpart T)
Commercial
Diving supervisor — overview of duties
- The supervisor is appointed in writing and is in immediate control of the diving operation.
- Confirms the team is competent, medically fit and correctly certified for the work and the diving mode.
- Verifies plant and equipment are suitable, maintained and checked before use.
- Briefs the team on the plan, hazards and emergency procedures, and maintains communication with every diver.
- May stop the dive at any time for safety, and the decision is not to be overruled.
- Ensures the diving operations record and each diver's logbook are completed and signed.
- Exact legal duties vary by country and client — read the regulations and codes of practice that apply to your job.
Sources: UK HSE — Diving at Work · IMCA — International Marine Contractors Association · OSHA — Commercial Diving Operations (29 CFR 1910 Subpart T)
Recreational
Flying and altitude after diving
- Flying or driving to altitude soon after diving increases the risk of decompression sickness.
- DAN publishes consensus guidance on minimum surface intervals before flying; longer intervals are recommended after multiple days of diving or decompression dives.
- Check the current DAN guidance and your training agency or company rules — they may require longer intervals.
- If you have any symptoms of DCS, do not fly: seek medical advice first.
- Commercial and saturation divers must follow their company procedures and the advice of a diving medical physician.
Sources: DAN — Flying after diving · Divers Alert Network (DAN)
Technical
Oxygen exposure limits — the concept
- Oxygen becomes toxic at raised partial pressures: to the central nervous system (CNS) at high ppO2, and to the lungs with long exposures.
- Exposure is tracked as ppO2 versus time; NOAA published widely used single-exposure and daily limits.
- The 'CNS %' and OTU/UPTD figures shown by computers and planners are estimates, not guarantees — toxicity can occur below the limits.
- Your ppO2 limits are set by your training, your operations manual or your supervisor — this app does not choose them for you.
- Factors such as exertion, cold and CO2 retention increase risk.
Sources: NOAA Diving Program · DAN — Health & Diving resources
Technical
Gas analysis
- Analyse every cylinder or supply before use — never trust a label alone.
- Calibrate the analyser as the manufacturer instructs (commonly against air or pure oxygen) and check sensor age.
- Record the measured fraction(s), the maximum operating depth, the date and the analyst's name on the cylinder label and the log.
- Trimix requires helium analysis too; commercial operations also check CO/CO2 and contaminants per the applicable standards.
- If the analysis does not match the plan, do not dive that gas — re-plan or replace it.
Sources: NOAA Diving Program · IMCA — International Marine Contractors Association
General
Buddy and standby diver
- Recreational buddies: agree the plan, signals, gas turn points and separation procedure before the dive.
- Stay close enough to reach your buddy and share gas within seconds.
- Commercial standby diver: fully dressed, checked, briefed on the task and ready to enter immediately.
- The standby diver's gas supply is independent of the working diver's supply where the rules require it.
- A tender must monitor each diver's umbilical and communications at all times.
Sources: ADCI — Association of Diving Contractors International · UK HSE — Diving at Work · NOAA Diving Program
General
Hypothermia and thermal protection
- Water removes body heat far faster than air; long or deep dives can cause hypothermia even in warm water.
- Warning signs: persistent shivering, clumsiness, confusion, slurred speech, poor judgement.
- Abort the dive if you are getting cold — cold also impairs decision making and may increase DCS risk.
- After the dive: get out of the wind, remove wet clothing, rewarm gradually and seek medical help for moderate or severe cases.
- Plan suitable exposure protection, and hot-water suits or heated gas where the operation requires them.
Sources: DAN — Health & Diving resources · NOAA Diving Program
General
Barotrauma — signs to watch for
- Ear and sinus squeeze: pain, fullness, hearing loss, vertigo or nosebleed. Never force equalisation; abort if you cannot equalise.
- Mask squeeze: red eyes, facial bruising — exhale through the nose on descent.
- Pulmonary barotrauma (lung over-expansion) can follow a breath-hold or rapid ascent: chest pain, shortness of breath, coughing blood, or stroke-like signs.
- Any neurological symptoms after surfacing are an emergency — give oxygen and call emergency services.
- Do not dive with a cold or congestion; see a doctor before diving again after a significant barotrauma.
Sources: DAN — Health & Diving resources · Divers Alert Network (DAN)
General
Decompression sickness — symptoms and first aid
- Possible symptoms: unusual fatigue, joint or limb pain, skin rash or itching, numbness or tingling, weakness, dizziness, breathing difficulty, confusion or paralysis.
- Symptoms usually appear within hours of surfacing but can be delayed; assume DCS if in doubt.
- First aid: give the highest concentration of oxygen available and monitor breathing. Position per DAN: a responsive diver in the recovery position (on one side, head supported) or reclined comfortably; an unresponsive diver who is breathing in the recovery position; an unresponsive diver who is not breathing on their back for CPR (drowning: 5 rescue breaths first). Keep them warm and handle gently.
- Call local emergency services and a diving emergency hotline (e.g. DAN Emergency Hotline +1-919-684-9111) for advice and the nearest chamber.
- Do not attempt in-water recompression and do not apply treatment schedules — definitive treatment is decided by a qualified hyperbaric physician.
- Record the dive profile(s), gases and symptom times and send them with the diver.
Sources: DAN — Decompression illness · DAN Travelers Medical Guide 6.2 — Rescuing divers and swimmers (positioning) · Divers Alert Network (DAN)
Commercial
Log-keeping and diving medicals
- Commercial divers keep a personal logbook recording every dive; each entry is signed by the supervisor.
- Record date, location, diving mode, gas, maximum depth, bottom time, decompression carried out, work done and any incidents.
- Keep an in-date diving medical from an approved examiner; renewal intervals depend on the regulator (often yearly).
- Report any illness, injury or medication to your diving doctor and supervisor before diving.
- Retain logbooks and medical certificates — clients and auditors routinely ask for them.
Sources: UK HSE — Diving at Work · IMCA — International Marine Contractors Association · ADCI — Association of Diving Contractors International
Commercial
Permits and standards — an overview
- IMCA publishes international codes of practice and guidance widely used offshore (e.g. IMCA D 014).
- ADCI publishes the International Consensus Standards for Commercial Diving and Underwater Operations.
- In the USA, OSHA regulates commercial diving under 29 CFR 1910 Subpart T; the US Coast Guard covers some vessel-based operations.
- In Great Britain, the Diving at Work Regulations 1997 and HSE Approved Codes of Practice apply.
- Many countries have their own regulator; clients may add stricter requirements — always check which rules govern your job.
- Obtain official copies from the publisher — do not rely on summaries (including this one).
Sources: IMCA — International Marine Contractors Association · ADCI — Association of Diving Contractors International · OSHA — Commercial Diving Operations (29 CFR 1910 Subpart T) · UK HSE — Diving at Work
Hyperbaric
Saturation and chamber operations — overview
- Saturation diving keeps divers under pressure for days to weeks; they decompress once at the end.
- Life support technicians monitor chamber gas, temperature, humidity and hygiene around the clock.
- Only trained, certified personnel may operate chambers and life-support systems.
- All procedures — including decompression and emergency hyperbaric evacuation — come from the approved company manual and the supervisor.
- Fire is a major chamber hazard: control oxygen levels and materials taken inside.
Sources: IMCA — International Marine Contractors Association · UK HSE — Diving at Work