Heart Rate Question

I may have gone into pure over-kill at the gym today! According to my hrm, my heart rate was up to 181 (with my max being 187). Everything I have read online says that 80-90% of max for short spurts is ok, but I have found nothing about getting up to 97%. I actually feel fine and definitely burned some calories today, but I was just wondering, is 97% of your max safe for maybe 30 seconds at a time?