Dead Space is a defunct, or shall we simply say “dead,” survival horror game that enthralled computer game players from 2008 to at least 2013. Sadly, the company that designed the horrifically beautiful game, Visceral Games, is no more. It has been, so to speak, eviscerated.
The main protagonist of the Dead Space Series was Isaac Clarke. If I was a game player I think I would be an Isaac fan since he was one of those rare Clarke’s known as a “corpse-slaying badass.” If in some unforeseen future my survival depended on being such a slayer, I’d want to be badass about it too, just like Isaac. As they say, anything worth doing …
Isaac Clarke and his Dead Space world make a great segue to introduce another matter of personal survival. And that is DEAD SPACE in underwater breathing equipment.
Clarke has proven to be equally at home underwater and in space due to his interesting cyan-lighted helmet. (I’m not sure where his eyes are, but perhaps in the 26th century a multi-frequency sensor suite makes a simple pair of eyes redundant.)
Historically, the U.S Navy used the venerable MK 5 diving helmet and the MK 12 diving helmet, which although they had no sensor suites, at least allowed divers to work at fairly great depths without drowning. However, they shared a common problem: Dead Space. 
In ventilation terms, dead space is a gas volume that impedes the transfer of carbon dioxide (CO2) from a diver or snorkeler’s breath. When we exhale through any breathing device, hose, tube, or one-way valve we expect that exhaled breath to be removed completely, not hanging around to be re-inhaled with the next breath.
But a diving helmet inevitably has a large dead space. The only way to flush out the exhaled CO2 is by flowing a great deal of fresh gas through that helmet. A flow of up to six cubic feet of gas per minute is sometimes needed to mix and remove the diver’s exhaled breath from a diving helmet like the MK 12.
In more modern helmets, the dead space has been reduced by having the diver wear an oral-nasal mask inside the diving helmet, and giving the diver gas only on inhalation using a demand regulator like that used in scuba diving. The famous series of Kirby Morgan helmets, arguably the most popular in the world, is an example of such modern helmets.
Full face masks are used when light weight and agility is required, as in public service diving, cold water diving, or in Special Forces operations. The design of full face masks (FFM) has evolved through the years to favor small dead space, for all the reasons explained above.
Erich C. Frandrup’s 2003 Master’s Thesis for Duke’s Department of Mechanical Engineering and Materials Science reported on research on a simple breathing apparatus, snorkels. You can’t get much simpler than that.
Frandrup confirmed quantitatively what many of us knew qualitatively. Snorkels are by design low breathing resistance, and low dead space devices. 
Happily, the dead space can be easily calculated, as simply the volume contained within the snorkel.
Surprisingly, some snorkel manufacturers have recently sought to improve upon a great thing by modifying snorkels, combining them with a full face mask. The Navy has not studied those modified snorkels since Navy divers don’t use snorkels. However, you don’t get something for nothing. If you add a full face mask to a snorkel, dead space has to increase, even when using an oral-nasal mask.
So what?
In 1995 Dan Warkander and Claus Lundgren compared the dead space of common diving equipment, including full face masks, and reported on increases both in diver ventilation and the maximum amount of CO2 in the diver’s lungs. Basically the physiological effects of dead space goes like this: we naturally produce CO2 during the process of “burning” fuel, just like a car engine does. (Of course our fuel is glucose, not gasoline.) The more we work, the more CO2 we produce in our blood, and the more we have to breathe (ventilate) to expel that CO2 out of our bodies.
If we are exhaling into a dead space, some of that exhaled CO2 will be inhaled into our lungs during our next breath. That’s not good, because now we have to breathe harder to expel both the produced CO2 and the reinhaled CO2. In other words, dead space makes us breathe harder.
Now, if we’re breathing through an underwater breathing apparatus, hard breathing is, well, hard. As a result, we tend to get a little lazy and allow CO2 to build up in the blood stream. And if that CO2 get high enough, it’s lights out for us. Underwater, the lights are likely to stay out.
In a computer game like Dead Space, no one worries about helmet dead space. But if a movie is ever based on the game, whichever actor plays Isaac Clarke should be very concerned about the most insidious type of Dead Space, that in his futuristic helmet. It can be (need I say it?) — deadly.
