I was just on an airplane tour in an old biplane (1920s or so, with an open cockpit). The plane was very loud, but I didn’t cover my ears because I didn’t think it would muffle the sound that much. When we landed, the pilot asked me why I didn’t cover my ears. I said I didn’t think it would make a difference, and the guy got all annoyed at me and said if I got hearing damage from the plane trip, it wasn’t his fault (meaning don’t sue him). This creeped me out a bit - how could 15 minutes of exposure to a loud noise cause hearing damage? Is there any truth to what he said?
Sure. I had a friend have an M-80 go off right next to his ear and he couldn’t hear anything out of one ear for a week, while the other on buzzed constantly. That was only for a split second. Fifteen minutes could do some mild damage. It may wear off after a week or so, but next time, make sure you have some.
If a sound is loud enough, then 15 minutes will certainly be enough. Generally speaking, sound intensities greater than 80 dB can cause hearing loss.
Permissible levels of noise exposure in the workplace have been defined by the U.S. Department of Labor in 1969, and OSHA made it their standard in 1971. Beyond these levels, hearing protection becomes necessary.
Permissible Noise Exposure as a function of duration
[ul]
[li]90 dB…8 hours[/li][li]95 dB…4 hours[/li][li]100 dB…2 hours[/li][li]105 dB…1 hour[/li][li]110 dB…1/2 hour[/li][li]115 dB…1/4 hour or less[/li][/ul]
What this means is that in the workplace, someone can be exposed to an average of up to 90 dB without the requirement for hearing protection. (Hearing conservation programs in the workplace often kick in at the 80 dB level).
Exposure to loud noise for any length of time has the chance of inducing a temporary shift in hearing sensitivity. Once a temporary shift occurs, it then becomes likely that the shift may become permanent unless steps are taken to reduce the exposure, either through hearing protection or by removing yourself from the source of the noise.
The insidious thing about noise-induced hearing loss is that damage can occur to your hearing without any pain. If your ears are hurting due to loud sounds, you are well past the point where permanent noise-induced hearing loss can occur.
One thing I should add: wearing earplugs or hearing protection does not make you immune to loud noise. It simply prolongs the amount of time you can be exposed to that loud noise.
The chances are very good that your friend suffered some permanent hearing loss in that ear, given your description of the case. It sounds like the initial blast caused an immediate temporary threshold shift, and some, but perhaps not all, of the shift was resolved later on. In other words, there may have been a permanent shift, but it may have been mild compared to the degree of the temporary shift.
He ought to seriously consider getting his hearing checked by an audiologist.
Okay, so I guess my question should’ve been - how loud is a rotary engine from a 1929 biplane? (a New Standard D-25, to be specific).
I went to a local fair where they had a monster truck on show. Now this wasn’t the kind where you sat in a grandstand to watch but one where the truck went around the field for people who wanted to ride in the back. Anyway, the engine wasn’t really loud that it was annoying just a deep rumble. Well, the next day my ears were ringing and little painful. With some average conversations and sound then it went back to normal later that day but it was strange in the morning. Yes, you might not think the sound is hearing your ears but it definitely could be with little or no pain from it at first.
Well, not being too familiar with airplane engines from that time period, I really don’t know for sure. If you want to know exactly, you can use a sound level meter to measure the sound intensity of the engine. I’d do the measurement in the cockpit, since that’s where the pilot and passenger is located.
To give you a ballpark idea of typical intensities of some environmental sounds, here’s a list I once made for a presentation, based on a source that I can’t locate now. I think the distance from the sound source here is assumed to be 10 feet.
[ul]
[li]10 dB…Normal breathing[/li][li]30 dB…Humming[/li][li]40 dB…Soft whisper; refrigerator[/li][li]50 dB…Moderate rainfall, car horn[/li][li]60 dB…Dishwasher; speech[/li][li]70 dB…Hairdryer, noisy restaurant, small party, TV[/li][li]80 dB…Vacuum cleaner, washing machine, garbage disposal[/li][li]90 dB…Lawn mower, motorcycle, blender[/li][li]100 dB…Garbage truck, wood shop, pneumatic drill[/li][li]110 dB…Chainsaw, headphones, stereos over 100 watts, rock concert[/li][li]120 dB…Snowmobiles, thunderclap[/li][li]130 dB…Ambulance siren[/li][li]140 dB…Firecrackers, jet take-off, fire siren, gunfire[/li][li]180 dB…Rocket launching pad[/li][/ul]
I think it’s safe to guess that if you’re close enough to a rocket launching pad to experience 180 dB, hearing loss will be the least of your concerns. 
First of all - the dork pilot in the OP should have been offering some sort of ear protection to his passengers. How rude. Disposable ear plugs, headphones, whatever. Creep.
Prop plane engines range considerably in noise generated. The quietest one I fly is supposedly 72 decibels. A circa 1929 biplane is going to be a LOT louder. Hearing loss used to be an occupational hazard of pilots from WWI through the 1960s. It still happens to some of them.