Specialized is definitely preferred over special. Using Special here would mean 'unusual or unique in some way', whereas specialized means 'made with a particular, specific usage in mind'. You could have "special glasses" that are special because they used to belong to some celebrity; but if you have "specialized glasses", they are not just ordinary "correct your vision" glasses but have some additional feature or capability that makes them useful in some narrower function; for example, they could be UV-resistant or heat-shielded.
Worn vs. used is more of a toss-up; if most of the gear being discussed is actually placed on your body and carried about like an article of clothing (and performs its protective function while doing so), then worn is fine. If some significant portion must be carried around, then placed somewhere and set up before you use it, used could be more suitable. Since the sentence talks specifically about "clothing or equipment", you could use both words: "...clothing or equipment that is worn or used by employees..."
Security vs. safety depends on the nature of the hazards that the gear is intended to protect against. Safety is a broader range and is probably suitable for any protective gear; Security implies that the hazards being faced are due to hostile agents attempting to harm you. (I would tend to think in terms of protection from gunshots/knives/blunt trauma for security, whereas safety could include protection from fire, slipping, acid, smoke inhalation, and any other environmental hazards.)
