84dB is well into severe but the "definition" is based on the average of both ears across 250Hz, 500Hz, 1kHz, 2kHz and I think 4kHz so it's a bit of a fudge. Depending on how the frequencies are spread out you can have Moderate to Severe implying you've got a mix of both.
http://www.batod.org.uk/index.php?id=/resources/audiology/descriptors/audiometric-descriptors.htm US and UK definitions differ slightly - mileage varies across Europe too no doubt. I tend to assume no one is wrong, just different ways of the same thing.
I wonder if you had some pre-existing loss as well as accident related damage although if your YACF age is accurate you're awful young for that. What did the audi-torture bods say? Ask them if they haven't told you. Also ask for a copy of your audiometry, it's invaluable as evidence and also being able to link up information about deafness/hearing loss to your experience.
There are two main kinds of hearing loss.
1) Conductive which means something has affected outer ear, ear canal or middle ear.
2) Sensori-neural which means something has affected the cochlea or the auditory nerve to the brain.
You can have both types of loss at the same time.
Where the losses are also matters. High frequency losses affect consonant sounds such as
K SH F TH S G CH and make English harder to make sense of. Other languages have different key frequencies. I can't recall where you are based - I seem to recall it's not in the UK. Lower frequencies affect
vowel sounds and D B NG J Z so loss of these can result in distortion to what you hear especially if there is poor acoustics (lower frequencies are harder to acoustically dampen)...
An audiogram is plotted on a X axis of frequency in Hz and kHz vs "volume" in dB (Decibels). There be trippy logarithmical wossnames with sound volumes so it's not intuitive. 100x louder is 20dB; 24x louder is 12 dB - I still don't understand the maths! Different sounds are in different loudnesses and frequencies on an audiogram chart see
http://www.barakta.org.uk/stuff/hearing/SMALLaudiogram-template.png for examples of speech sounds and every day noises. Audiometry tells you that you can hear a tone at X frequency at Y volume.. It doesn't tell you how well you are processing speech or if you have some degree of distortion. More info on reading audiograms at
http://www.hearingdirect.com/pages/Audiograms-Explained.html and easily googleable with "audiogram explained" which will get you examples which might look familiar to you.
Hearing aids are not like glasses, they do not totally correct hearing loss/deafness. Hearing through hearing aids is different to natural hearing but I can't comment as I have always used hearing aids. You will almost certainly lose things like "cocktail party effect" which is the ability to pick out one sound (signal) in a noisy background environment (noise) e.g. restaurant or dining hall. Hearing people with normally working ears are using minute differences in when the sound hits each ear to do amazing cognitive processing which hearing aids can't yet fully do.. They're getting there, especially if you get two which speak to one another properly... You may well get directionality if not true stereo/other effects.
You will need a higher signal to noise ratio to pick up a desired sound (signal) in amongst undesired sound (noise). This means noisy places become even more difficult for you than before. You can sometimes learn to lipread/read other clues but it may always remain harder work.
Widex are an excellent hearing aid brand, many of the experienced deaf folk I know use and like them a lot. There's a whole range of peripherals such as
http://www.widex.co.uk/en/products/accessories/dex/ which can connect to bluetooth, fm, TV, phone etc... I know folk who rate them highly but they are not cheap. If you are in the UK and employed you can weasel funding from employers for some of this sort of stuff. Otherwise there isn't really funding for this. These can be helpful in conference style situations.
Agree with others about batteries, you'll probably end up with orange tabbed 13 size batteries, they're the most common. It's always useful to clock other hearing aid users just in case.
When you get your aids, don't be afraid to keep going back until things are right. Earmoulds should not hurt and if they rub they can quickly cause damage which is hard to heal and will deteriorate easily. It can feel like you're making a fuss but you really aren't. Same for programming, if you find the aids are UNBEARABLE with certain sounds, make a note and speak to the audiologists as they can probably link that to frequencies and do lots of tweaking.
I agree with Kim on lipreading and or sign classes and if you let me know where you are based I will see what your local hearing loss organisations are - they can be useful for meeting people for advice and ideas and stuff.
The hearing aid protectors Kim referenced are called Ear Gear as at
http://www.deafequipment.co.uk/catalogue/1233614/Ear-Gear And for lolz my audiometry is at
http://www.barakta.org.uk/stuff/hearing/SMALLNatalyaAudiogramtextsmall.png The blue is what I can't hear even with hearing aids.
White + Blue is what I can't hear with hearing aids out (usual audiometry readings).
I have a mixed deafness which means both my middle and inner ear are affected.