Although the situation is a bit unusual, the legal Q it raises is a common one. Let me break it down.
As you know, employers must accommodate disabled employees to the point of undue hardship. As a general rule, an accommodation constitutes undue hardship when it would put other workers (or third parties like visitors or people near the site) in serious danger. So the first thing you’d need to determine is whether the firefighter’s hearing problems are posing such a danger. Without knowing all the facts, I’d say they are.
Result: You probably don’t have to let him keep doing the job unless the hearing problem is addressed, e.g., he gets a hearing aid. Having co-workers use hand signals may also work although that wouldn’t solve the traffic danger. Normally, you’d also have to explore reassigning the employee to a less safety-sensitive position but that’s probably not the case since this is a volunteer firefighter.
But there’s also a second part of complying with accommodations duties, namely, following the right accommodations procedures. That would include doing a medical assessment and attempting to find an accommodation that’s suitable to his capabilities and needs.
BTW, if your Q is literally, “has anybody else had to deal with this?”, let me know and we’ll set this up as a Survey. glennd@bongarde.com. One way or another, I hope this helps. Glenn