How can a manual fire alarm be activated?

A manual fire alarm can be activated through a specific action that is directly intended to signal an emergency. Using a fire alarm switch serves this purpose, as it allows a person to manually trigger the alarm system in the event of a fire or smoke situation.

When someone observes a fire, they can quickly and effectively use the switch to inform others in the vicinity and initiate the proper emergency response. This method of alerting is critical because it is designed for immediate human intervention, ensuring prompt notification to occupants and emergency services.

The option regarding breaking an emergency glass also pertains to manual activation, as many fire alarm systems include pull stations behind glass that need to be broken to activate. However, the inclusion of the term "emergency glass" specifies a particular design, whereas the fire alarm switch is a more general term for various activation methods.

The other options, such as the presence of a large amount of smoke or calling the fire department, do not directly activate a manual fire alarm system. Smoke may trigger an automatic alarm, but does not require human action in the same way. Calling the fire department is a response to an emergency, rather than an activation method for the alarm itself.