As SCUBA divers go deeper underwater, the pressure from the weight of all the water above them increases tremendously which compresses the gases in their blood. What happens to the volume of gas in their blood as the diver rises quickly to the surface?

 The volume of gas expands because of the decrease in pressure as he tries to exit the water body, therefore he must take necessary precaution.

Explanation:

Using Boyle's law which states that the  the pressure of a given mass of an ideal gas is inversely proportional to its volume at a constant temperature

ie P1VI=P2V2

A diver absorbs compressed nitrogen gas when  he dives into the water body, As he ascends  out of the water body having less pressure, the volume of nitrogen gas which he absorbs will tend to expand following  Boyle's Law.  Therefore a scuba driver should not rises quickly but slowly  to the surface or else the  expanding nitrogen gas can cause tiny bubbles in his blood and tissue to form together with joints pains and eventually  cause decompression sickness needing medical attention.