News
Rebreather Pre-Dive Checks
The following is a discussion and review of the subject of Pre Dive checks when diving rebreathers – a much discussed, varied and often controversial matter!
When we first learn to dive, the concept of a buddy check, pre dive check or safety drill is installed in us as a means to make the dive safer by spotting potential problems before they can manifest and potentially evolve into accidents.
This is not a procedure limited to diving, it is extremely common in the Aviation, Aerospace and military communities, but to bring it closer to home it is present when we drive a car. When we drive a simple, mainly mechanical, car we are aware of the pre drive steps of checking the coolant level, the tyre pressures and the oil level and then adjusting the seat, wing and rear view mirrors to the individual driver. In a more modern, computer controlled car, many of these checks may be completed by the control system and communicated to the driver via dash board instrumentation and at the high end, even the seat and mirror settings can be altered to individual drivers with the push of a button. What is most common is a combination of automated computer generated checks and manual human checks; either way we are assured of the functionality of the vehicle before heading out on the road.
With rebreather technology the source of the pre dive check sequence and method could come from a variety of places. The manufacturer of the specific rebreather, a training agency that teach a specific rebreather, a generic training agency rebreather check list to suit all rebreathers and a learnt acronym to prompt the required checks.
Of course it would be best if available to use the specific rebreather check list or system supplied by the manufacturer.
Within the above there are different ways to complete checks:
- A written check list
- A check list acronym – e.g a common rebreather check list reminder is the acronym of F.L.A.G.S.
- Flow
- Loop
- Analyse
- Gauges
- Stack/Sensors
- Electronic check lists within the rebreathers display
- Electronic check lists that analyse data from the actual components of the rebreather.
What should be checked?
Pre-Assembly
Mushroom (One Way) Valves. The one way check valves within the Mouthpiece assembly that ensure the gas flows around the rebreather in a single correct direction should be tested to ensure they open with and close against FLOW.
The Oxygen, Diluent, Single supply gas and all bailout cylinders for the planned dive should be ANALYSED.
The absorbent canister (STACK) should be either re-packed or replaced. Or the used time of a previously used canister should be noted and the remaining time available compared to the dive plan.
Pre-Dive
There are as many pre dive check sequences as there are rebreathers, in fact many more! So for initial discussion of the steps of pre dive checks we will here use the acronym FLAGS as a starting point. Although not exhaustive if the printed check sheets or on screen check prompts of most of the currently available rebreathers are reviewed all steps within them can be classified under one of the following prompt words:
F – FLOW
Ambient pressure gas flow around the rebreather in a single correct direction. Tested with the Mushroom (One Way) valve check as part of Pre Assembly. This should be tested prior to each dive as stray granules of absorbent etc could compromise a Mushroom Valve.
High pressure and intermediate pressure gas flow around the rebreather. Slowly turn on the cylinder valves and then add Diluent and Oxygen manually, inflate and check dumps on BCD/wing, check that the ADV and BOV function and ensure the solenoid can inject oxygen where applicable to each specific type of rebreather.
L – LOOP
Conduct a negative loop test and a positive loop test where appropriate to each style of rebreather.
A negative test is conducted on a completely assembled rebreather by placing the mouthpiece in the rebreather or closed circuit position and breathing in through the mouth (To empty the loop) and out through the nose until the loop is empty and then closing the mouthpiece. A suitable period of time (A minimum of 1 minute) is allowed to pass and the rebreather should maintain that negative i.e. not leak air into to rebreather.
Indications of a good negative can include, crushed breathing hoses, ADV diaphragm remaining concave or in, a lower PO2 than ambient (e.g. Pre negative mouthpiece open PO2 0.21, during negative mouthpiece closed 0.19) and a strong ‘gasp’ or sucking sound when opening the mouthpiece at the end of the check.
A positive test is conducted on a completely assembled rebreather by placing the mouthpiece in the rebreather or closed circuit position and breathing in through the nose and out through the mouth until the loop is full and then closing the mouthpiece. A suitable period of time (A minimum of 1 minute) is allowed to pass and the rebreather should maintain that positive i.e. not leak air out of rebreather.
Indications of a good positive can include rigid inflated counter lungs.
A – ANALYSE
The Rebreather although containing Oxygen sensors must not be used to analyse the gases used within the rebreather.
All gases, Oxygen, Diluent and all bailouts should be analysed and labeled prior to being assembled into the rebreather or as bailouts with an Oxygen or where required an Oxygen/Helium analyser.
Many rebreathers are calibrated by flushing them completely or flushing a sensing chamber where the sensors sit with Oxygen at Ambient pressure, if this were completed with a gas supply other than specified (i.e. Oxygen) then the calibration would be inaccurate and therefore the PO2 incorrect during the dive.
G – GAUGES
Test the contents of all required cylinders, Oxygen, Diluent and all required bailout and check for leaks.
Turn on (Slowly) cylinder valves and note the reading of pressure.
Turn off cylinder valves and leave off for 1 minute.
Check contents pressure has not dropped (If the pressure has dropped there is an HP or IP leak to be located and resolved)
S – STACK / SENSORS
The rebreather should be tested for basic function by the Pre Breathe detailed below.
The purpose of this check is to watch the 3 sensor outputs for stabilisation, correct reading and change on prompt i.e. whist breathing add Oxygen and note a rise in PO2 and then add Diluent and note a drop in PO2 from set point.
If fitted during the Pre Breathe a Carbon Dioxide sensor can be monitored for a rising figure.
Again if fitted on the specific rebreather a thermal activity monitor ‘Temp Stick’ can be monitored to ascertain the exothermic reaction of the sofnolime absorbing Carbon Dioxide causing thermal sensors within the stack to register a rise in temperature.
Pre-Breathe
The fully assembled Pre Dive checked rebreather should be breathed for an adequate time to assure the user of systems functionality.
This is the period when the above Stack/Sensors tests are performed.
Current research would indicate that a part used, over used, poorly packed, incorrectly fitted or even absent stack may not give enough signs or symptoms of Hypercapnia during a 3-5 minute Pre Breathe to ensure a diver notices and considers the rebreather unfit for use.
Quick Pre Jump Confirmation
Many training agencies provide Pre Jump quick check prompt cards that can be attached to the Rebreather.
Steps on these include but are not limited to:
- Cylinder valves fully open on Oxygen, Diluent, Single supply gas and bailout?
- Electronics on and safe breathable PO2 displayed?
- BCD inflated?
- Mouthpiece in mouth and in rebreather position?
These Pre Jump checks are NOT considered a full Pre Dive check and are in no way meant to replace full Pre assembly, Pre Dive and Pre Dive checks. The Pre Jump is intended to be used in addition to normal checks as a last check just prior to water entry.
Find out more about Phil at www.philshorttechnical.co.uk.
With over 40 years of experience, Westfield Sub Aqua and Marine Insurance Services provides specialist travel insurance. Whether you’re heading on a scuba diving trip, cruise, or a ski-holiday, we offer tailored cover to keep you protected. in addition many other activities can be included for your peace of mind.
These policies are competitively priced and comparable to that of Standard Type Travel Insurance.
Specialist cover available for:
- Scuba Diving Holidays
- Cruise Ship Holidays
- Skiing Holidays.
- Golf Holidays.
- Many other Sporting Activities can be included.
- Annual Multi Trip Polices up to the age of 85.
- No Age Limits on Single Trip policies.
Many Pre-Existing Medical conditions can also be covered.
Top Tip Checklist
- The cover period must be the full duration of your trip. (i.e the date you leave your home to the date you return back to your home)
- Check the Cancellation and Curtailment levels suit your needs. (i.e reducing this can reduce the premium)
Adjust the Excess Levels to see how you much you could save.
Get an online quote from Westfield Sub Aqua and Marine Insurance today at westfield.b2ctravel.co.uk/quote or call 01483 237827.
Green Fins National Workshop Charts Roadmap for Sustainable Marine Tourism Initiatives
Green Fins, the global environmental standards for diving and snorkelling, is set to contribute to Indonesia’s blue economy. A national workshop, focused on “Enabling a sustainable diving and snorkelling industry in Indonesia through the implementation of Green Fins initiative,” has ignited a collaborative effort to safeguard the nation’s marine ecosystems through marine tourism.
The Reef-World Foundation, the UNEP Coordinating Body on the Seas of East Asia (COBSEA) and the Coral Triangle Center (CTC) held the Green Fins National Workshop in Aryaduta Menteng, Jakarta, Indonesia, on 18 – 19 February 2025. This pivotal event, supported by IUCN (International Union for Conservation of Nature) through the Blue Natural Capital Financing Facility (BNCFF), brought together key stakeholders from the Indonesian government, marine tourism industry, conservation organisations and the global Green Fins network to develop a roadmap for strengthening the Green Fins initiative in Indonesia and to explore sustainable financing mechanisms for its long-term implementation.
Participants from five Indonesian ministries, including the Ministry of Marine Affairs and Fisheries and the Ministry of Tourism and Creative Economy, collaborated with local MPA management bodies, dive operators and international experts to chart a course for a more environmentally responsible marine tourism sector. This diverse group engaged in focused discussions and strategic planning, addressed key aspects of Green Fins implementation and explored opportunities for its integration into national marine conservation efforts.
“We’re not just discussing sustainability”, said JJ Harvey, Operations Director at The Reef-World Foundation. “We’re creating a tangible roadmap for action. The energy and collaboration at this workshop have been truly inspiring, laying the groundwork for real, measurable change in Indonesia’s dive industry and unlocking the full potential of its marine tourism while ensuring the future health of its reefs.”
“The Coral Triangle, as the global epicenter of marine biodiversity, relies on Indonesia’s leadership to combat threats through strong coral reef conservation and sustainable tourism practices,” said Rili Djohani, CTC Executive Director. “Expanding Green Fins and scaling up training efforts are crucial steps toward ensuring equitable benefit-sharing and long-term conservation impact of our unique marine resources.”
“Sustainable Blue Economy is at the forefront of COBSEA’s work on marine and coastal ecosystems,” stated Mahesh Pradhan, UNEP COBSEA Coordinator. “Ensuring sustainable practices in marine ecotourism in Indonesia and the East Asian Seas region will further consolidate concrete conservation efforts while also benefiting local communities. COBSEA is proud to support the Green Fins initiative, which was initiated in Thailand over 20 years ago and has now blossomed into a significant global movement.”
Key discussions and explorations during the workshop included:
- Alignment of Green Fins with national policies and international commitments, including the Indonesia 2030/45 MPA Vision, the national biodiversity action plan (NBSAP) and international commitments such as the Global Biodiversity Framework.
- Exploration of a comprehensive roadmap for Green Fins implementation in Indonesia, outlining potential steps, timeline and financial strategies.
- Discussions on diverse financing mechanisms, including public-private partnerships, blended finance models, and integration with existing programmes, to ensure the long-term financial sustainability of Green Fins.
- Emphasis on enhanced collaboration between government agencies, the private sector and conservation organisations.
- A strong focus on inclusivity, including gender-inclusive approaches and support for small-scale businesses.
The workshop highlighted Indonesia’s position as a global leader in MPA-based diving, with 70% of dives occurring within MPAs. Discussions emphasised the need to address challenges such as revenue leakage and high implementation costs while leveraging opportunities to integrate Green Fins into existing government initiatives, such as the Ministry of Marine Affairs and Fisheries’ Blue Economy strategy and the Ministry of Tourism’s sustainable tourism programmes. Participants also engaged in a learning exchange, sharing best practices from countries like the Philippines, Malaysia, Japan and Thailand, focusing on developing sustainable funding models and enhancing assessor capacity.
The outcomes of this workshop will both strengthen Green Fins Indonesia and contribute to the broader global impact, driving sustainable marine tourism worldwide.
Discover how your organisation can contribute to the global expansion of Green Fins by contacting info@greenfins.net.
About Reef-World
The Reef-World Foundation is a registered UK charity which delivers practical solutions for marine conservation around the world. The charity promotes the wise use of natural resources – particularly coral reefs and related ecosystems – for the benefit of local communities, visitors and future generations. It is dedicated to supporting, inspiring and empowering governments, businesses, communities and individuals around the world to act in conserving and sustainably developing coastal resources.
Reef-World leads the global implementation of the UN Environment Programme’s Green Fins initiative, which focuses on driving environmentally friendly scuba diving and snorkelling practices across the industry globally. As such, the charity provides low-cost and practical solutions to local and industry-wide environmental challenges associated with the marine tourism industry. It provides education and capacity-building assistance to empower environmental champions (within the diving industry, local communities, authorities and governments) to implement proven coastal resource management approaches.
Please visit www.reef-world.org to learn more or follow us on Facebook, Instagram and X.
About Green Fins
Green Fins is a proven conservation management approach – spearheaded by The Reef-World Foundation in partnership with the UN Environment Programme – which leads to a measurable reduction in the negative environmental impacts associated with the marine tourism industry. The initiative aims to protect and conserve coral reefs through environmentally friendly guidelines that promote a sustainable diving and snorkelling tourism industry. It provides the only internationally recognised environmental standards for the diving and snorkelling industry and has a robust assessment system to measure compliance.
Green Fins encourages and empowers members of the diving industry to act to reduce the pressures on coral reefs by offering dive and snorkel companies practical, low-cost alternatives to harmful practices – such as anchoring, fish feeding and chemical pollution – as well as providing strategic training, support and resources. By reducing the local direct and indirect pressures tourism puts on coral reefs, it helps make corals healthier and more resilient to other stresses, such as the effects of climate change. Look for the Green Fins logo when booking your next dive trip.
Please visit www.greenfins.net to learn more or follow the initiative on Facebook, Instagram and X.
About Coral Triangle Center
Coral Triangle Center (CTC) is a foundation based in Indonesia with regional scope and global impact. Established in 2010, CTC works closely with local communities, private sector, governments, and partners to strengthen marine resource management in the Coral Triangle to protect coral reef ecosystems, ensure sustainable livelihoods and food security.
CTC supports on-the-ground conservation in Bali, Maluku, as well as in Timor-Leste, and leads learning networks of women leaders and marine protected area practitioners in Indonesia, Malaysia, Philippines, Papua New Guinea, Solomon Islands, and Timor-Leste. CTC is developing its Center for Marine Conservation in Bali as an integrated learning space for training programs, outreach activities, interactive exhibits, and artistic and cultural performances to influence millions of people to care for our oceans and those who depend on it.
Since its establishment in 2010 until 2024, CTC has protected more than 435,000 hectares of critical marine habitat. We have trained more than 8,000 people to support marine protected areas and sustainable fisheries management throughout the Coral Triangle region. More than 26,000 people have visited our Center for Marine Conservation, many of whom have been inspired to take direct action to protect our oceans. In the last three years, we reach an average of 200,000 people annually to care for our seas via our social media channels.
About UNEP COBSEA
The Coordinating Body on the Seas of East Asia (COBSEA) is a regional intergovernmental mechanism and one of 18 Regional Seas Programmes. It is the decision-making body for the East Asian Seas Action Plan, bridging together nine countries – Cambodia, China, Indonesia, Republic of Korea, Malaysia, the Philippines, Thailand, Singapore, and Viet Nam – in the protection and sustainable development of the marine and coastal environment for the health and well-being of present and future generations. The COBSEA Secretariat is hosted by Thailand in Bangkok and is administered by the United Nations Environment Programme (UNEP).
COBSEA works on 1) marine pollution prevention, reduction and control, 2) marine and coastal biodiversity, ecosystem conservation and management, and 3) climate action.
Gear Reviews2 months agoGear Review: SurfEars 4
- Blogs2 weeks ago
GO Diving Show 2025: The Monster Mark Evans Created (And Why the Industry Loves It)
- News4 weeks ago
Humpback Mother and Calf Win Underwater Photographer of the Year 2025
- News1 month ago
Go Diving Show 2025 Exhibitor Showcase
- Marine Life & Conservation4 weeks ago
ARC marine Celebrates “Commended” Award at Underwater Photographer of the Year with reef cube image
- News2 months ago
2-for-1 tickets now available for GO Diving Show
- News1 month ago
Filming 360 in The Bahamas
- News2 months ago
Exclusive Shark Diving Adventure in the Maldives – Last Female Space Available!
