I had some long discussions about this topic last year on a list serve for a service dog group (including breeders, puppy raisers, and graduates who use service dogs), in CCS, among members, and with a member of the Committee on Chemists with Disabilities. The bottom line is that you cannot legally refuse to allow the dog into lab, as it is as much part of the person as a wheelchair or a hearing aid (always assuming it is a legitimate service dog). However, it is honestly not in the best interests of the dog, that student, or others in the lab to allow it in, and every effort, in my opinion and that of most others in the service dog community, should be expended to find an alternative to meet the student's needs.
What are the hazards in the lab? Mention was made of vapors, broken glass, and spills. As an instructor for over 40 years in gen chem, these are real concerns. Yes, we use hoods (hopefully) as much as possible, but my students were weighing out naphthalene for a lab last week and the vapors permeated the entire lab. Spills have a habit of spreading if they involve liquids, and solids may "drift" to the floor in all kinds of unexpected places. Even if your students are neat and never have a spill, there is no way of knowing what is on the floor or bench from other labs. Broken glass is obvious - splinters are dispersed over a wide area.
In addition, there is the issue of the physical location of the dog. Some (definitely not all) service dogs will lie quietly in one place for 3 or 4 hours, but even then they will move a bit, as you would if you had to sit in a seat for 4 hours without getting out of it. Dogs have tails and legs which extend from their bodies, and which obviously can be stepped on. If someone inadvertently steps on the dog's extremities, any dog will react and may cause the person to move suddenly, dropping or splashing what she is carrying, with possible harm to the student, neighbors or the dog.
We require all visitors to a lab to wear splash goggles, but the dog's eyes are unprotected. We should require closed-toe shoes and protection for the body (lab coat or apron), but the dog's body is unprotected. This is truly an accident waiting to happen.
What happens in case of an emergency? A fire alarm goes off and students quickly leave the lab, hopefully in an orderly fashion. How does the dog react to the alarm? How quickly can the student retrieve the dog? Will that dog impede exit from the lab?
Another question is what the dog can do for the student in the lab. Service dogs are trained to pick up objects from the floor, to carry them to their partners, to turn on switches, open and close drawers and doors, help remove or don clothing, among others. Which of these services are needed in the lab? If the student needs help with clothing or backpack, that could be done before entering the lab. A "hearing" dog may alert a student to sound, but so can a lab partner. A "seeing eye" dog will help the student with a visual impairment, but it certainly cannot help carry out the lab experiment, and moving around the lab with such a dog would be a potential hazard for all others in the lab.
Let me give you some background on me as it relates to disabilities and service dogs. I have two paraplegic daughters and have been involved in the disabled community for over 25 years. I am also a puppy raiser for a service dog organization, charged with the basic training of such a puppy from the age of 2 months to approximately 20 months. As such I take my puppies to my classes, professional meetings, movies, restaurants, stores, even on planes and public transportation - but not in a lab, even an empty lab. I know many people of all ages who have a wide variety of service dogs, and I know what these dogs can do for their partners. I also know students in the lab, after over 40 years of college teaching, and the way in which something can go wrong with a normally safe experiment.
I would urge that the dog be left outside the lab and that the student's lab partner, a TA or instructor, or a personal aide provide the services needed. Where to leave the dog? I have a portable crate in my office for times when my puppy has to be left alone without supervision, and she is perfectly happy to go to sleep in it. This could be in the hall or a nearby office or space external to the lab. If absolutely necessary, the crate could be in a corner of the lab, although for many of the reasons above I think this is not very desirable.
Again, bottom line is the dog cannot be banned from the lab. However, since every person I know with a service dog cares intensely for that dog's well-being, explaining the reasons for not wanting the dog in the lab and providing adequate help for the student will most probably result in the dog not coming in.