Can methane gas emit from a shower without a ptrap?

Do you mean to say sewer gas?

And if there is no trap between the shower and the rain stack... then yes sewer gas WILL as there will be nothing stopping it.

Hi Mthompso

Yeah, all kinds of hazardous stuff associated with sewer gasses, including methane gas!

Click on this link for more information:

Sewer gas - Wikipedia, the free encyclopedia

If you can't get a trap to the shower then I know of an alternative that may help... just let me know that you are interested, OK?

Mark