The oil safety switch is operated by _____.

The oil safety switch is designed to monitor oil pressure within a heating system, particularly in oil-fired heating applications. It serves a critical function by ensuring that the oil pressure remains within safe operating limits. If the oil pressure drops below a certain threshold, the switch will activate, typically shutting down the system to prevent potential damage or unsafe operating conditions.

Monitoring oil pressure is vital because low pressure can indicate insufficient fuel supply, which could lead to incomplete combustion and result in hazardous conditions like system damage or carbon monoxide production. Therefore, the correct answer highlights the primary role of the oil safety switch in protecting the system from failures associated with inadequate oil pressure.

In contrast, elements such as oil temperature, system humidity, and airflow rate do not directly trigger the operation of the oil safety switch. Oil temperature relates to the viscosity and performance of the oil, while system humidity and airflow rate are separate factors that pertain to the overall efficiency and performance of the HVAC system but are not directly linked to the function of the oil safety switch.