BECAREFUL when using Ear Muffs at the same time you are using Safety Glasses. Some Studies have shown up to a 60% reduction in the Noise Reduction Rating for certain muffs when used in conjunction with safety glasses. The problem is the seal around your ear canal can be greatly comprimised by the ear piece of the glasses. Just something to think about...the manufacturer of your muffs should be able to answer any questions.
