A manual fire alarm system must be installed in Group F occupancies when the combined occupant load is what number or more?

In Group F occupancies, which typically include factories and similar types of industrial buildings, a manual fire alarm system is required to be installed when the combined occupant load reaches or exceeds 500 individuals. This requirement is based on safety regulations that account for the potential risk of fire in these environments, where the presence of machinery and combustible materials can increase the likelihood and severity of fires.

The threshold of 500 occupants is significant as it strikes a balance between ensuring safety through adequate fire alarm systems and not overburdening smaller facilities that may not need such extensive systems. At an occupant load of 500 or more, the building's evacuation plan and response to fire emergencies become crucial, thus warranting enhanced safety measures such as manual fire alarms to alert occupants effectively and facilitate a quicker response from emergency services.

The other numbers provided do not meet the regulatory threshold established for this specific occupancy type, as lower occupant loads may not necessarily trigger the same level of risk assessment required for larger gatherings in industrial settings.