The term "exemption" is misleading.
There is no way to legally "exempt" a worker from the required protective measures. Not for his/her comfort or convenience and not for the company's.
However, nothing prevents an employer from relaxing the use of PPE if it isn't really required. Mike gave a couple of good examples of that.
Most nuke plants have a comprehensive rule that you wear Hardhats, Safety Glasses, Work Shoes, Gloves, and Hearing Protection any time you are in the power block - even if no hazards exist. Then they write you up a form which "exempts" you from this rule as long as you are in an area with no hazards and your work doesn't create any hazards.
I like to make the analogy to entering the RCA. Imagine that every time you signed into an RWP you had to wear double cloth PC's, a plastic coverall, a tyvek coverall, double gloves, double shoe covers, an air-line respirator and an ice vest. Then when you get to your work area, the HP tells you what you can take off.
Sounds stupid, huh? Well, PPE isn't as drastic. Wearing a hardhat and safety glasses and carrying gloves and ear plugs is not nearly as burdensome as all that. So, they just make it a blanket requirement.
This all works well until it gets abused. It gets abused a LOT. Many times, the supervisor bypasses the Job Safety Analysis, which is required for every job - especially one with a PPE exemption, and goes right to signing an exemption just because the workers asked him to.
In order to establish the PPE requirements for any area, whether it is to add or remove them, you must analyze the work area for hazards. First, you check the environment, then you analyze the actual work process. You must provide some approved protective measures against all hazards. If you want to substitute another protection, it must meet the ANSI standard or it must remove the hazard entirely.
I have heard every excuse. Most of them are stupid.
There is NEVER a reason to exempt safety glasses. All the reasons for doing so go right out the window as soon as somebody walks on the refuel bridge wearing his own prescription glasses. If those are OK on the bridge, then all glasses are OK. If they are new and clean, they will not impair vision. If they are an FME concern - use a lanyard. If they fog up - use ventilation. etc. etc. etc. You would never tell someone to take off his prescription glasses because of these things, so you have no justification for telling him to remove his protective glasses either.
A face-shield is never a substitute for safety glasses. Any job that requires a face shield also requires either safety glasses or goggles as well. The flimsy contamination barrier that HP supplies to keep zoomie dust off your face has ZERO impact protection and is not ANSI approved. Bubble hoods are not approved eye protection.
Hardhats are not an FME problem. They float. They are too big to fit into most piping systems or get lost in the fuel. they are easy to see and easy to retrieve. If they get contaminated, they can be wiped clean. If they can't be wiped clean, they can be replaced. You can buy a new one for under ten dollars. If they fall off, you can put on a chin strap. (In over twenty-five years of wearing a hardhat at work - even inside a submarine - I have NEVER had one fall off unless it was knocked off, in which case it was good that I was wearing it to protect me from the thing that knocked it off.)
Earphones and face shields are available that fit onto hardhats. The fact that the wrong ones were bought does not give a license to exempt hardhats just because these are in use.
So, I'll tell you straight. You can never "exempt" PPE. If you are sure that you have no hazards, or if you can remove them, or if you can establish an approved alternative method to protect against them, then you can show that PPE is not necessary. But if you cut the tiniest of corners, and exempt something that could protect someone, and someone gets hurt, you have done that person a grave disservice as well as exposed your employer to the liability that comes with failing to protect a worker against injury.
I know the babies will cry. A lot of times they will argue that PPE or fall protection or a safe work practice is more dangerous than not using it. they are wrong. They mix up things that are uncomfortable, time-consuming, difficult, or expensive with unsafe. Nukes get things twisted even further. You need to protect the PEOPLE first, then the fuel - period. Being contaminated is not dangerous. You have to decon people with contaminated chins. You have to fill out forms, and maybe calculate a skin dose or do a WBC. You get a head laceration in a contaminated area, and you have to do all that PLUS it gets on the evening news, PLUS the NRC starts asking questions, ... Ask yourself which is worse to deal with - a contaminated chin, or a contaminated bleeding head. There is NO (zero, zip, nada) job in this world other than lifesaving itself that justifies exposing human beings to injury. Melted metal that ejects neutrons can be a problem (a HUGE problem) but it doesn't measure up to blinding or paralyzing a single person. I spend a lot of my time defending my decision to deny waivers and exemptions, and it makes the workers angry. There is no financial penalty to me for making someone angry that he has to do his job safely. I used to sign these things all the time. Now, I know a lot more than I did then.
Of course, it seems as though I am at odds with my dear friend Cathy. Actually, she makes the best point of all. Remove the hazard. If contamination is the hazard - decon. If falling is a hazard - build scaffold with rails. If falling objects are the hazard - do the work elsewhere or construct a barrier. Remove as many hazards as you can FIRST. Then you can start looking at PPE requirements.
I know this homily is a little long. But I really believe in my work. The "short" answer (as always) is: it depends. Now, you know what it depends on. No two situations are identical, so no single answer can be correct. You have to take each situation as you find it. No hardhats at a control point might sound like an easy one. But, then the carpenters show up and start building a scaffold next to it. No glasses on the fuel bridge? Until a cable snaps and flings little pieces of wire into an eye. Get the picture? You can write these things all day long, but something will eventually bite you in the ass.
"OK, this one should be simple - " Yeah, you might have thought so, huh?