How can I prevent a gas embolism while scuba diving?
Besides remembering not to hold my breath. I’m afraid I will forget so to be extra safe, I thought if there was a maximum depth or something where gas embolisms become very unlikely, I’d only scuba to that depth.
Thanks.
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Tags: diving, embolism, Prevent, scuba
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Good luck with that. You are actually at more risk of air embolism in shallower depths than you are at deeper depths because the relative change in pressure increases as you near the surface.
To understand this, suppose that you are at 99 feet of depth in the ocean with your lungs slightly less than 75% full of air. At that depth the absolute pressure is 4 atmospheres (ata). Suppose you then hold your breath and ascend 33 feet so that you are now at 66 feet, where the pressure is 3 ata (a 25% reduction in pressure). Since volume is inversely proportional to pressure, the volume of air in your lungs is now 4/3 of what it was at 99 feet, which is just under 100% (75/3*4=100). Your lungs would probably not rupture since your lung volume is just under its capacity.
Now assume that instead of starting at 99 feet, you start at 33 feet with your lungs slightly less than 75% full and ascend the final 33 feet to the surface while holding your breath. At 33 feet the pressure is 2 ata while at the surface it is 1 ata (a 50% reduction in pressure), so the air volume in your lungs doubles from near 75% capacity to near 150% capacity. Since this far exceeds your lung capacity of 100%, your lungs rupture and causes an air embolism. Don’t forget that you ascended the exact same distance (33 feet) as you did when going from 99 feet to 66 feet.
Hopefully this helps illustrate how relative pressure change increases in shallower depths. It is even possible to cause a lung overexpansion injury in very shallow water, since the tissue surrounding the microscopic gas sacs (alveoli) that make up our lungs can rupture with only a 1.5 psi increase in internal pressure. This means that filling your lungs to capacity and ascending as little as 4 feet while holding your breath can cause the tissue to rupture.
The right answer here is not to be as concerned about limiting your depth as you should be about resolving to NEVER hold your breath while ascending. The reason that most people ‘forget’ this rule is overwhelmingly due to panic…so your best defense against an air embolism is to remain in control of yourself at all times no matter what happens. A calm, controlled reaction to even the most dire situation has a much better chance of a successful outcome than a panicked, knee-jerk response.
The safest thing you can do is not to hold your breath. You should have a depth gauge or dive computer. Check it often and make sure you don’t ascend to fast. If for some reason you must make an emergency ascent, you should exhale the entire time. Depth isn’t your real concern here, it is your rate of ascent. If you are not a student now, you can always take a refresher course to brush up on your skills or just to make sure you are comfortable and SAFE.