How many exits do you provide signs for?

Just the primary route? 

I work mainly I schools and have been told to only put signs on the primary routes, however if this route is blocked I don't know how a visitor would know the secondary route. But then if I sign a secondary route this may be confusing!

There are normally plans available, but these only show the primary routes, however I'm not sure if anyone would read them in an emergency.

I have checked BS9999 and Building regs B, but can't seem to find it.

BS 5499 part 4 says the primary escape route from each room to a final exit should be signed and if you have to make a choice, the shorter route should be choose, if they are both the same, distance then both should be signed. Because you have to assess from each room, then each room will have its own primary escape route which means all escape routes would need signing.

I think it is important that unfamiliar escape routes should be signed but if you follow the guidance of the BS then it is more than likely that all escape routes will be signed anyway.