one other thing to add.....say you have 500 people on one floor and 3 exit stairs. In order to calculate the required stair widths and door widths do you divide that 500 by 3? Or do you have to be more specific, like if there is a higher occupancy in one part of the floor, those stairs should be larger?
thanks

Cascading (adding occupants from each level as you travel down the exit path) has not been a part of the UBC/IBC since the 70's. Sizing an exit is based upon the worst case load at that exit - you'll find that most code calculations are based upon sizing for the worst case or combination of factors.

It may be prudent to apportion occupants to certain exit to accomodate anticipated occupancy conditions - but at the same time, like I mentioned above, you need to make sure that you're considering the worst case combination.

question 1, you do not add occupancy unless the egress converges. for example a sub floor converging withth egress of the ground floor. in that case you add the occupancies. otherwise, it's per floor as you go down.

question 2, you do not divide evenly by 3. you have to disect the building by occupant load going through that door. this number has to do with egress path, number of interveining rooms, use, etc. so it cannot be answered specifically.

i would look in your office for a good approved cd set. a good cd set will have a narrative on how to follow all the different tables to check your egress requirement are correct, and have the drawings to go along with that. there's not really a rule of thumb. there are tables and a specific procedure to follow to check it.

also keep in mind there is a minimum width. if you have 3 means of egress, and that puts you below the minimum width, you still need to have the minimum width.

thank you guys, great advice