An employee applying pesticides with the signal word "DANGER" may work alone at night if they:

The situation requires that an employee applying pesticides with the signal word "DANGER" maintains safety oversight while working alone, especially during night hours. The correct answer emphasizes the necessity for communication with a responsible adult. Making personal contact by radio with a responsible adult every hour ensures that someone is aware of the employee's status and can respond quickly in case of an emergency. This communication protocol is a critical safety measure that helps mitigate risks associated with pesticide application, which can be hazardous.

Maintaining contact ensures that the employee is not isolated, facilitating timely assistance should any complications arise during their work. This requirement is aligned with industry regulations that prioritize worker safety, particularly in high-risk situations like handling highly toxic substances. In contrast, the other options discuss permits, location, or training, which, while important in different contexts, do not address the immediate safety concern of having a communication link during solitary nighttime activities.