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What is the (supposed) reason for the FFM? We don't prevent convulsion drownings by slapping a FFM on, we prevent convulsions by properly managing oxygen exposure. The following text was a reply I posted to someone on Rodales (a recreational board), of all places. This FFM nonsense has no business being discussed by persons on technical diving lists who should know better. As with everything else -- think it through. -Sean >> Exactly what are your reasons for wanting to use a full face mask? These are dangerous pieces of gear which really should only be used when absolutely necessary. Circumstances that would necessitate a FFM are: 1) Swiftwater. A FFM with a five strap spider is necessary to keep the mask securely on your face, as a standard mask and reg would be ripped off in upper class (3+) swift water. 2) Blackwater. Absolute zero visibility presents the risk of impacting or entrapping objects which could dislodge or foul your mask or second stage. The FFM in this case provides greater security, as well as #3 below, commonly associated with black water. 3) Contaminants. The FFM reduces the risk of infection from low level water- borne contaminants, bacteria, etc. High level contaminants require complete hermetic isolation through the use of a vulcanized drysuit directly attached to a helmet with a double exhaust. 4) Hardwire comms. Obviously, when comms are indicated, they need to be hardwire for maximum clarity and reliability. FFM's allow the combination of mouth and nose in a single gas space for voice intelligibility. 5) Oxygen toxicity risk. The FFM will prevent drowing when an oxygen convulsion occurs. This is really only applicable when decompressing on pure oxygen after an exposure which justifies the risk. See below for explanation. Full face masks complicate gas sharing, hose routing, and emergency procedures. They increase your gas consumption, and are prone to freeflow. Using these in cold water makes little sense, as the increased freeflow probability incurred by using the FFM in turn increases the probability of freezing a reg. They shouldn't be used deep under any circumstances, certainly not where gas switches are required. Using a standard half-mask and reg, with proper exposure protection, the only part of your body which is even exposed to the water is your upper lip, and this is a very well perfused area -- meaning that metabolic heating prevents tissue damage from freezing. I have dove in the Canadian arctic with a standard half-mask and reg -- not an issue. Cumulative (pulmonary) oxygen exposure is not much of an issue on recreational dive profiles, and CNS toxicity is more appropriately managed by lowering the PPO2 of the gas you are breathing, rather than diving an elevated PPO2 and then worrying about convulsions. I have an AGA Interspiro MKII, and a ScubaPro FFM. I use the AGA when clear voice comms are necessary (hardly ever), and the SP in swiftwater due to its low profile, and the oral/nasal separation, which makes it easy to purge when it floods. Generally, full face masks present a risk which is not justified in day-to-day diving -- certainly not for recreational open water diving. They are important gear when necessary, but hardly ever necessary. -Sean Quoting Scott Hunsucker <shunsucker@co*.ne*>: > Curt, > I can see the use of FFM in certain limited situations, but I cannot > see it in use by the majority of people that may be inclined to buy one and > > use it at Peacock since they saw it on the dive-rite site. I would also > argue that the use of a block only increases the number of failure points > in a system. If one needed to switch regs through a FFM then M/F QDs > (similar to those used on the RB 80) could be employed w/o reliance on a > block to plug them into. > I was as alarmed by the advertisement of the FFM as I was by the other > items mentioned, hence its inclusion in the post. > I will also admit that since I only dive in caves my view of gear and > its applications is toward cave diving. I do realize that dive-rite sells > gear to many divers who do dive in a variety of environments and hence may > have a desire for such items. But dive-rite is historically directed at > cave divers and I didn't post my question to rec-scuba. > Scott > >Scott > > > >The use of FFM below 300 feet is a common occurrence for most commercial > >divers and technical divers who need the use of U/W communications to work > > >or direct projects. They are also used commonly in very cold water just to > > >help protect the face. > > > >Yes FFM use more gas, but typically just because of talking. I have > >noticed that if you do not talk they really do not use much -- Send mail for the `techdiver' mailing list to `techdiver@aquanaut.com'. Send subscribe/unsubscribe requests to `techdiver-request@aquanaut.com'.
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