Electronic Comm Systems and Their Weak Link (Hint: It’s You!)
by Mark Phillips
Recently, we had a long conversation in our Public Safety Diving group about full face masks and underwater communication systems.
One of the discussions was about the difference between hardwire and wireless systems. The differences were well explained but no one touched on one of the failure points of these systems. Communications systems can, do, and will fail at some point in time. The majority of the time it is not the equipment; it is the user that caused the problem.
When we start to lose clear communication, or our wireless communications fail, it is usually either a battery issue or a microphone issue. Problems attributing to the battery can be easily resolved by simply making it a standard practice to replace the battery before every mission.
When I teach full face mask classes, I emphasize that the correct time to don one is before you enter the water and the correct time to take it off is when you have exited the water. How many times have you seen teams drag their FFMs through the water or take them off and drop them in the same water they are diving in – and later complain about how nasty the water was to dive in.
If we forget about the contamination factors or even the microparticle inhalation of that same water, do you know what is happening to your full face mask and communications system?
In Public Safety Diving, electronic communications systems are either hard wired or wireless systems.
In the Public Safety Diving community and recreational market, wireless seems to be the most common. Those who dive the wireless system dive with the ME-16R Hot Mic. If you look at the mic in your FFM and it is RED, it is probably the ME-16R. Hardwired systems may have the SuperMic.
While the Hot Mic can be swapped out on a dive site by removing two screws, if the SuperMic fails, it must be sent back to the manufacturer for repair or replacement. The SuperMic is waterproof but does not provide the same quality of sound and does not share the same noise canceling properties of the Hot Mic. That is the tradeoff for being a hardened and waterproof mic.
The habits and assumed permissions that allow you to drop your FFM in the water or drag it through the water are not easy to break. There are as many excuses as there are divers for why it happens and why it is OK – but it is not.
It is a problem.
Not only are you contaminating your mask, you are potentially damaging the microphone you depend on for communication.
To prevent any presumed bias or more “here he goes again”, the following is from the manufacturer:
ME-16R Hot Mic (150 Ohm)
How does it work? A special membrane is used on both sides of the diaphragm which allows air, but not water, to enter. This allows the microphone to cancel noise that is more than 1/4″ away. Noise such as air, bubbles, and breathing sounds are virtually eliminated. This is especially noticed when using a full-face mask with an oral-nasal cavity. We have been contracted many times to help produce TV and/or Motion Pictures when studio-quality sound is a must.
Can the microphone element be damaged? Yes, the microphone has its limitations. The membrane is designed to allow a user to take the mask off at the back of the boat while in the water. In the past, microphones being exposed to seawater had a short life. Also, when cleaning a ffm, water damaged the old style microphone elements, not so with a Hot Mic. However, the Hot Mic® element can only withstand a differential pressure of about 12′. This means if a diver takes off the ffm at the back of the boat and drops down to 15′, the membrane will not be able to keep the water out and the microphone element will be damaged. In our tests, we made several dives to 35′ and took off an AGA ffm with a Hot Mic. After putting it back on and clearing it, communications were fine. However, if you took the full face mask off at 35′ and dropped down to 47′, the membrane would be compromised. We also found if you expose the Hot Mic at any depth down to 130′ and come up, no damage will occur.
Conclusion: The Hot Mic will give you the finest intelligibility available and last for months with little maintenance.
For even more explanation,
The Hot Mic is a two sided microphone. One side is a mylar membrane and the other is a hydrophobic membrane. These membranes “waterproof” the microphone, with the breathable hydrophobic membrane allowing the airspace inside the mic to equalize as the equipment is taken to depth. This limits the depth that the mic can be taken while flooded. In other words, you cannot flood the mask and go deeper than about 12 to 15 feet before the microphone is compromised. Either the Mylar will rupture or the hydrophobic membrane will sweat water through damaging the microphone element.
What this means is simple – if you get the microphone wet and increase the pressure around it by 5 to 7 pounds, you will damage the microphone. If you do it enough it will fail. While not delicate, if you hit the mic with a pressure washer or fire hose, you will likely damage it. Once the membrane in the microphone becomes wet, increased pressure will damage the microphone.
At this point, common sense should prevail but then again, how many divers do you see trailing their FFM behind them as they enter or leave the water? One of our main topics of discussion within the Public Safety Diving community is full encapsulation protection from contamination. Yet the device we use to provide protection from exposure to our face and provides our supply air is often soaking in the very water we are diving in.
Perhaps the smell and taste of diluted sewage is appealing?
“No Bobby, that was not a pinecone…”
Though you may be ok doing ditch and don drills in a pool or open water training, the microphone still should not be soaked. The pressure difference that can affect a Hot Mic can occur in a 12 -15’ deep swimming pool. The deep end of a swimming pool may be 9 or 10 feet and may be a marginal risk to the microphone membrane.
Considering how important they are to the functionality of your communications systems and how much they cost to replace, you might take the time to remove them before training FFM ditch and don. Not only will this keep them dry while you train, it will provide you an opportunity – a reminder – to inspect and clean the interior of your mask beyond a quick rinse and hang dry.
Replace the battery in the earpiece before every dive mission. Keep extra batteries for all your communications units on hand as well as any tools that may be necessary to change them quickly. Keep extra microphones in stock with your save a dive kits. Remember to keep the tools necessary to remove and replace a microphone with them. It takes a couple of minutes to put in a new battery and even swap out a microphone. If one or the other does not correct the problem, you have a problem greater than can be addressed on your dive site.
Always have a backup plan practiced, verbalized, and in place before starting a dive. Be prepared if or when your communication system fails.
Full Face Masks work very well and offer a great deal of protection to our divers – but only if used correctly. Your Full Face Mask should be donned before you enter the water and removed when you have exited the water. Follow this simple rule and your Hot Mics will provide longer service life and better communications.
Are you interested in taking a full face mask course? Learn more here: https://www.tdisdi.com/erdi/get-certified/erd-full-face-mask-ops/