I'd be as concerned about a potential rip in the bag compromising the success and comfort of your own experience. Please use a brand new bag, as in a turkey roasting bag you buy in a 2-pack at the grocery store. I cannot overemphasize the importance of carefully following the comprehensive instructions provided in fightingsioux's inert gas thread (plug his name into the search block above), to include leaving room at the opening for excess helium to escape as it also keeps the bag inflated. No rips should result. Your cats should be fine, provided you aren't in a small, enclosed space with them. Leave a window cracked, and ensure your body is found within several hours--both for the sake of your pets AND for friends/loved ones who find you. Orpheus, if you have any doubts regarding your decision to ctb, then by all means, wait. Reflect and take all the time you need to be sure. The helium/exit bag technique, if executed properly (as fightingsioux describes), is NOT a mere suicidal gesture or experiment. You are beyond the point of no return after 8-10 seconds. Be sure. Wishing you peace.