API 520
a. A relief valve is a spring loaded pressure relief valve actuated by the static pressure upstream of the valve. The valve opens normally in proportion to the pressure increase over the opening pressure. A relief valve is used primarily with incompressible fluids.
b. A safety valve is a spring loaded pressure relief valve actuated by the static pressure upstream of the valve and characterized by rapid opening or pop action. A safety valve is normally used with compressible fluids.
c. A safety relief valve is a spring loaded pressure relief valve that may be used as either a safety or relief valve depending on the application.

Returning to my question :
Is it possible to use Safety-relief valves in gas services?
If yes, how is their reaction to pressure excess, do they pop-up like safety valves or gradually open?