Is listening daily at an average of 85db safe?

Not a problem provided it is music. This is not loud at all. If this were machinery for 8 hours a day then the answer might be different.

It makes no difference whether it is music or a finely-tuned machine, like a HD...a dB is a dB.

It does. A machine at 85 db will output continuous noise at that level affecting the ear in exactly the same frequencies for a continuous period - like a jack hammer on the hearing it is specifically working certain nerve bundles and hairs.

Music (especially classical) will have much more dynamic range - so you get a lot of soft passages mixed with louder ones that may reach 85 db only on the louder passages.

The key with hearing is exposure. Giving your ears a break is very important. That break can be either several soft classical passages or an album of laid back acoustic music played in the middle of a session or harder and louder rock.

Variety is important - 4 hours of continuous Metallica played loud is much worse than an eclectic mix with some balads thrown in.