Is exercising at a pulse rate of 180 dangerous for a fit 47 year old male? I exercise daily

Its close. Your maximum target heart rate is 220 minus your age; this would put you at 173. If you are a begginer to exercise you should gradually work up to this level and this of course assumes you do not have cardiac problems. If you do consult your physician to determine a safe level to start your exercise program.
Exercise. I doubt there is much benefit to sustaining a training rate of 180 compared to 150-160. Mixing in intervals up to 180 might be a benefit. If you are not training for some important goal but primarily for health, i would recommend the lower range.