Safety training usually focuses on content, and making sure people "go through" the training at the prescribed intervals. Unfortunately, there are trainee issues that are often overlooked: vision and hearing impairments, literacy and language issues, developmental and learning disabilities, and learning styles.
The biggest problem is that many trainees either are in denial about their communication difficulties, or are unaware of them. There are techniques safety trainers can use to make sure that all the information is accessible to every trainee without making an issue of hearing or visual problems.
Hearing loss is a particularly severe problem for safety professionals, as so many people are in denial about their problem. Much of this is psychological, but it is also impossible to tell what sounds you aren't hearing. We know for sure that hearing loss is increasing, and one survey by the Education and Auditory Research Foundation found that fully half of the 76 million -- that makes over 38 million -- baby boomers are having difficulty with hearing loss. Only one third have had their hearing tested.
You should assume that some of your audience members cannot hear well. Never offer anything verbally that isn't also available simultaneously visually. If you use a video, insist that either it be open-captioned or that, if it is close-captioned, the captioning be turned on every time it is shown. If you get a request from people to do something to help them hear, then do it! Even if it "cramps your style," as some speakers have complained to me when I asked them to wear an assistive listening microphone or stay at the stationary microphone, remember that if you refuse you have told that person that you don't deem them worth the bother of training or communicating with. Trust me, that person will return the favor and pay no attention to you, either!
And never, ever, under any circumstances, decide to speak over some "soft" background music! It takes very little to make what you say completely incomprehensible to a hard of hearing audience member.
There is one exception to this: if your presentation is real-time captioned. This is an importantoption to consider if you have more than 100 people in the audience, and if the training is really crucial. (Yes, all safety training is crucial, but where life, limb, the environment and public safety can be involved, you have a greater burden.) A specially-trained court reporter will type up what you say and either project it on a screen or let the one or two people who admit needing it read off their laptop screen.