The janitor of the student apartment of Petroleum University is an important post responsible for ensuring the safety of the student dormitory, and needs to be on duty 24 hours a day. Therefore, the doorman can't sleep at night, and must stay awake and respond to emergencies at any time. In addition, the duties of the janitor in the student apartment of Petroleum University include patrolling and checking the identity of visitors. This requires a high degree of vigilance. If the doorman sleeps during the duty, it may affect the safety of the student dormitory and have a negative impact on the doorman's own work. So the doorman in the student apartment of Petroleum University can't sleep at night.