Many employers looking for part time temporary staff do not have the facilities to safely insure an employee with specific needs.
It is a harsh reality that it would simply cost a lot more in terms of time and money. This is fine for a permanent position in a skilled job, but unrealistic for a temporary, part time job in a company that has a high turn over.
In my company we have blind and visually impaired people working on switchboard and data inputting (specialised equipment, obviously) and people with hearing problems working with computers and deliveries.
It is also true that colleagues have to be aware of their needs and adjust their behaviour accordingly. It is no good talking to a deaf person without getting their attention first, or waving to a blind person.