A manual fire alarm can be activated by which of the following methods?

A manual fire alarm can be activated by using a fire alarm switch, which is specifically designed for this purpose. This switch is a physical device that individuals can pull or press to manually initiate the fire alarm system, alerting everyone in the vicinity of a potential fire hazard. It ensures immediate notification to all building occupants and can facilitate a prompt response to evacuate the area or address the fire threat.

The other options provided are not methods for directly activating a manual fire alarm. A large amount of smoke may trigger an automatic fire detection system but does not serve as a means to manually activate an alarm. Breaking the glass of a fire extinguisher casing is not related to activating a fire alarm; these two devices serve different functions in fire safety. Calling 911 is a response action rather than an activation method; it alerts emergency services but does not sound the alarm within a building. Understanding the specific way to activate a manual fire alarm is crucial for ensuring safety protocols are effectively followed in emergency situations.