A Roll Call Has Its Limitations
Roll calls are used when people are assembled in an area after evacuating a building to check whether all those who were inside are now stood in the emergency assembly point and so have safely evacuated the building, meaning that they are not trapped in there and requiring rescue.
The roll call needs to know who was present in the building and who was not to be effective, which relies on the perfect operation of a signing in and signing out process. Unfortunately this has its limitations as it is going to be highly unlikely in all but the smallest of companies. People will forget or simply not be bothered to sign in and/or out at times. Even the introduction of electronic cards in some organisations which require the card to be swiped before the door will open and a person can enter or leave will still not be 100% accurate as people may be able to borrow the card of a colleague if they misplace or leave their own at their desk, or "tailgate" in which they follow close behind a person before the door shuts and in doing so do not need to swipe their own card, and as such are not registered by the system as having entered or exited.
If somebody is on the list as being in the building but are not present in the assembly point, it will be unknown whether they are simply away from the site, or whether they are in fact trapped in the building and in real danger. This may mean that somebody goes in and searches for them, placing their own safety in jeopardy, when in actual fact there was no need to if the person is not there. Not only will a roll call need to cover workers, but also needs to include visitors to the site who would be in the building too.