Oh dear. Doesn't it sometimes feel like the world is attacking us? Like... five helicopters passing while windows are opened and you are distracted. Sounds about something that could happen to me as well, there has been some incredibly unlucky setbacks. I think it's just because the world is so very loud and we are well aware of it now.
Firstly, having windows open is
not your fault @lifeisover - it's a normal thing to do, it's not like anyone could have predicted this happening at the exact same time. We are not some perfect machines, we are humane. We make silly mistakes each day, which mostly include spilling something, getting a paper cut or putting our shirt on inside out.
The thing is that with tinnitus some things that aren't mistakes, aren't predictable... we still think we should be able to prepare, prevent and just succeed 100 % of times. Therefore I think it's important to accept that there will be setbacks and there will be mistakes. It's really, really hard and I don't know how, as self-blame is my favorite hobby. It never helps tho, does it.
Then back on to the actual consequences of this noise exposure. How near were the helicopters, prolly not very near to the building, right? If so, I think there is a good chance they were far enough to not cause damage. Another thing is, how long did this last? If it was just a moment and the helicopters were not right outside of your window, I'm again quite sure you are alright. If someone was standing at the launching pad of 5 helicopters without hearing protection, then of course it would be serious and s/he would need to be treated asap. Anyway, was there any further signs of damage, like ear fullness or muffled hearing?
Futhermore, I don't think you should be measuring T volume now, as it is likely to increase with panic. Depending on the answers to these questions, I'd rather suggest to distract yourself with masking noises and do something to comfort you. Whether it's your favorite movie or a stroll in the nature. Just doing something else than obsessing will help. Easier said than done, but just try - the smallest thing possible, to make yourself feel a bit more secure.