The OSHA standards are a good starting point. Factory workers aren't even required to wear ear protection if the average noise over their 8 hour shift is under

The OSHA standards are a good starting point. Factory workers aren't even required to wear ear protection if the average noise over their 8 hour shift is under 85 dB. For 95 dB it's something like 15 minutes. From what I understand (and from what I've experienced), the every day repetition isn't the issue, it's the sustained noise for long periods of time. 2 little noisy bursts a day that are hours apart just aren't going to affect anything.