At 85 dB you'll have hearing damage from long term exposure without hearing protection. Normally considered 8 hours a day 5 days a week. So 2000 hours in a year. Higher sound levels have a lower threshold so shorter times. 120 dB is the threshold of pain, so immediate hearing damage. Also, dB are a 10x log scale. So every 10 dB is an order of magnitude increase. So the siren is actually about 3000x louder than when you should start wearing earpro.