Below is a picture of a gas separator used for that exact situation.
Here is the website that describes how to make the separator.
http://www.qsl.net/w2wdx/aquaria/diyco2.html#6
scroll down to the section called Over Tolerance Pressure Release and Prevention Systems
Here is the website that describes how to make the separator.
http://www.qsl.net/w2wdx/aquaria/diyco2.html#6
scroll down to the section called Over Tolerance Pressure Release and Prevention Systems