Boyle's Law — What It Is and Why It Matters
Boyle's law states that at a constant temperature, the volume of a gas is inversely proportional to its pressure. In diving, this means that as a diver descends and pressure increases, gas volumes decrease — and as they ascend, gas volumes expand. At 10 meters (2 ATA), a volume of gas is half its surface size. At 30 meters (4 ATA), it is one quarter.
Boyle's law is the most practically important gas law in diving. It explains why you must equalize your ears and mask on descent (air spaces compress), why you must never hold your breath while ascending (expanding lung gas can cause lung overexpansion injury), and why buoyancy changes with depth (wetsuit and BCD gas volume compress and expand).
Learn More
Frequently Asked Questions
Why is Boyle's law the most important gas law for divers?
Because it governs every pressure-volume change you experience on every dive. Ear equalization, mask clearing, BCD inflation, buoyancy control, and the #1 rule of scuba (never hold your breath) all relate directly to Boyle's law. It explains why gas spaces in your body and equipment change size with depth.
Where is the greatest pressure change on a dive?
Between the surface and 10 meters. The pressure doubles in that first 10 meters (from 1 ATA to 2 ATA), which represents a 100% increase and the greatest volume change. This is why equalization problems and lung overexpansion injuries are most likely near the surface.
Affiliate Disclosure: DiveComputers is a participant in the Amazon Services LLC Associates Program and eBay Partner Network. Links on this page may earn us a commission at no extra cost to you.