As all doors in the external envelope of a building can be used as a final exit when do you not have to put a crash bar/push pad type mechanism on a main entrance door or other frequently used door to a school building?  E.g. some doors have a digital lock on them which has a lever handle internally.

A usual rule of thumb is if the route is used by 60 or more it needs to be panic proof (push bars) otherwise any normal emergency exit device (which includes lever handles as well as push pads) will suffice

Why then does one not normally see panic bars on main entrance doors?

Originally panic bars were only used in places of public assemble and where not used for normal access/exit, the main doors were used instead. As the main doors had to cope with the total occupancy, there was an extra amount of exit width and it  was considered the chance of a panic was low because of the choice of the number of exits available. In an emergency most would be exiting via the emergency exits where it was considered a panic might happen, so emergency exits were fitted with panic bars and not the main doors, but not always.

Over the years they started to be used in many buildings, usually on emergency fire exit doors which were only used for emergencies, now days  it is all about risk assessment and as a rule of thumb AB,s used by 60 or more is reasonable.

Thanks Tom, very useful info on background.  I'm not quite sure what you were saying in your second paragraph, can you clarify?

What I was trying to say was originally panic bars were used when it was considered that a panic could ensue in the event of an emergency, like places of public assemble, like theatres, cinemas, also doors to external fire escapes, but unclear why.

Then over time they started using them in places that really did not require them like on a door that was not on general use so an exit sign was fitted. Many people think because it has a fire exit sign it becomes a special emergency fire exit door but in fact all doors leading to safety, with or without signs are emergency fire exit doors in an emergency.

So I would consider AB rule of thumb, that they only needed on doors likely to be used by more than 60 persons and not always then, use risk assessment.