Had 5 of these doors in my previous organisation, (4 sliding horizontal to close and 1 verticle). These were classed as property protection and our insurers insisted that we closed them when the building was empty. (2 shift operation Monday to Friday). Apparently there had been instances where these doors had either failed to operate or not fully closed when triggered in a fire, therefore not giving the designed protection. We were told that by closing them at the end of the working day would prove that the mechanism works, with maintenance only required when identified through opening/closing them. We were also informed that we would invalidate the policy if there was a fire when the building was empty and the doors were not closed. Therefore we added opening and closing these doors to the opening-up / closing-down regime. When we first started this we ended up getting them serviced as they proved difficult to shut and would probably have failed to close if the fusible link had failed in a fire.