Gag Straps and CCRs

Are Mouthpiece Retaining Straps (MRS)—sometimes called gag straps—a good idea?
For recreational rebreather divers, the answer is likely no. More evidence could change my opinion here, but at present, any recommendation for MRS use is weak.

This topic was discussed at Rebreather Forum 4 (RF4), where the community debated whether MRS should be a standard safety feature. The consensus is:

The forum recognizes the use of correctly deployed mouthpiece retaining straps as a strategy for avoiding loss of the mouthpiece and minimization of water aspiration in the event of loss of consciousness underwater.

Attendees pointed out that even among the experts present, few actually used them in their own diving.

The Origin of the Recommendation

Much of the support for MRS comes from a French Navy study showing that divers fitted with these straps had a higher survival rate during incidents. Based on that data, the study strongly endorsed their use.

However, there’s a critical caveat. The divers in that study were operating at high oxygen partial pressures (PO₂)—levels above what recreational rebreather training agencies recommend and much higher than what civilian divers typically use.

Those elevated PO₂ levels greatly increased the risk of hyperoxia-induced seizures. In those situations, an MRS can help by keeping the mouthpiece in place if a diver loses consciousness.

Further, this study doesn’t control for other factors where a bailout is the correct solution. I call this the reverse survivalship bias. People who have managed failures on their unit with a quick bailout do not show up in studies.

For CCR divers diving within normal PO₂ limits (1.3 maximum), this risk-reward pathway doesn’t hold up. If your PO₂ management is conservative, the risk of seizure-induced loss of the mouthpiece is lower. The risk is never zero of course, and that’s an important thing to understand. It’s inappropriate to say proper Po2 management eliminates the chance of a seizure or hypoxic event. The rub comes in understanding how a MRS might cause unintended issues in other emergency scenarios.

Sometimes an analogy of a seatbelt is used. (In general, analogies are cheap ways to understand a situation and I don’t like them.) If we drive carefully, we still wear a seatbelt, because the chance of a crash is never zero. I think the more appropriate analogy is helmets in cars. Professional racecar drivers going 100mph+ need helmets because they’re increasing their risk of a crash significantly. Normal drivers don’t wear helmets though, because they’re mitigating risks of crashing in different ways. A helmet would be restrictive and cumbersome in your daily drive.

Understanding the Risks in CCR Diving

Closed-Circuit Rebreather (CCR) diving carries inherent risks that demand careful planning and streamlined responses. Common hazards include:

Hypoxia, hyperoxia, and hypercapnia (the “Three Hs”)
Chemical injuries
Static lung loading

In nearly all emergencies, the golden rule applies:

“Get off the loop.”

That means switching immediately to an open-circuit regulator. Any equipment that slows or obstructs this process increases the risk.

Bailout Strategies and Practical Realities

An effective bailout system allows a diver to reach breathable gas in a single, reliable motion. In theory, the best configuration is a Bailout Valve (BOV) connected to a large bailout cylinder, allowing instant switch-over to open circuit.

In practice, however, many BOVs are connected to small 3-liter cylinders-which isn’t enough gas. Divers often assume they’ll be calm enough to locate a secondary regulator afterward, but that’s an optimistic scenario while draining a small cylinder. Functionally, a small-tank BOV behaves no better than a Dive Surface Valve (DSV), and if inflation is tied into that cylinder, the setup can become even more dangerous.

BOVs also add weight, hose-routing complexity, and mechanical points of failure. They don’t help in every type of failure—particularly caustic floods, where the goal is to get the mouthpiece out, not keep it in. That’s why many experienced CCR divers still rely on a necklaced open-circuit regulator as a dependable bailout source – even with a BOV equipped CCR.

A DSV adds one extra step compared to a BOV—removing it before switching to the necklace—but that’s a reasonable tradeoff for simplicity and reliability.

The Problem with Skipping a Necklaced Regulator

Some divers forgo a necklaced regulator altogether, often to make it easier to pass a bailout cylinder to a teammate. While well-intentioned, this usually is a product insufficient bailout planning.

That choice adds several extra steps in an emergency:

Locate the correct bailout cylinder
Confirm the valve is open
Deploy any retainers or clips
Verify the correct regulator
Manage inline shutoffs if present

Even with training, this is a long chain of actions under stress. In a real emergency, every second counts. A necklaced regulator offers a direct, fail-safe path to breathable gas.

How MRS Affects Emergency Response

Adding an MRS introduces yet another step in the bailout sequence. Even a simple clip or buckle can create a critical delay. There have been fatalities where divers appeared to be mid-bailout but never completed the switch. This shows that they bailed out too late. Adding steps to access the bailout gas would not have resulted in a better outcome.

A BOV with an MRS might seem like a safe combination: if you lose consciousness, the mouthpiece stays in and the BOV can be turned to OC mode, allowing continued breathing. But the same setup becomes a liability in other emergencies. In a caustic flood, for instance, an MRS forces you to keep a corrosive mix in your mouth instead of spitting it out.

A DSV with an MRS is worse—it effectively straps the rebreather to your face, reducing your ability to escape from the breathing loop when things go wrong.

Some MRS are designed where a necklaced regulator cannot be used, because the mouthpiece must be moved down to get off the loop. A design like this, with a DSV, is the ultimate combination of additional steps to get open-circuit gas.

I’ve seen divers in real bailout situations where speed and access made the difference between survival and tragedy. Any delay—even a few seconds—could have tipped that balance.

Prevention Beats Reaction

Good diving safety depends on avoiding problems, not complicating responses to them.
The most effective risk mitigations are:

Conservative PO₂ management
Comprehensive pre-dive and build checklists
Continuous monitoring during the dive

These steps reduce the likelihood of ending up in a situation where an MRS might help—and also prevent many of the scenarios where it could make things worse.

The most useful input on this discussion at RF4 was this line advocating to test is the nay-sayers have any validity:

If the testing showed that bailout was not impeded by an MRS, then my opinion would change.

The current evidence that MRS help in high PO2 situations (and low PO2) is strong. The missing element is – how many people were able to bailout successfully in an emergency without an MRS where an MRS would have caused them to be unable to bailout.

Full Face Masks (FFM)

Often, the concept of a FFM comes up in this situation. I would not want people I love to dive with a FFM and a CCR. It’s like an MRS with more complexities and steps. Co2 retention, clearing, fogging, and bailout are all wildly more complex than mainstream configurations.

Conclusion

Mouthpiece Retaining Straps may make sense for military divers operating at high PO₂ levels, where unconsciousness from oxygen toxicity is a realistic concern. But for recreational rebreather divers, they introduce unnecessary complexity and slow down critical bailout actions. We should be open to data emerging that validate the use of MRS systems, but it is not convincing at this time.

Rebreather safety depends on prevention, simplicity, and rapid access to breathable gas. Anything that delays that process—no matter how well-intentioned—belongs on the “not worth it” list.