When does a Fire Sprinkler Flow Switch call the brigade?

For the purposes of this article and the use of flow switches in an automatic fire sprinkler system, we will focus on two variations of a wet pipe sprinkler system;

1. an automatic fire sprinkler system fitted with a water-motor direct brigade alarm ("DBA") or pressure switch ("PS") as the primary method for an alarm activation signal (DBA/PS Method); or
2. an automatic fire sprinkler system fitted with a water flow switch ("FS") that is used as the primary method for an alarm activation signal (FS Method).

The alternative to the aforementioned system arrangement is an automatic fire sprinkler system where one or more flow switches are used as the primary device to activate an alarm signal that is used to summon the fire brigade.

The two most common types of systems or applications of this arrangement are as follows;

• Class 9c, Aged Care Buildings or Class 2 / Class 3 Residential Buildings
• Combined Hydrant / Fire Sprinkler Systems

Class 9c, Aged Care Buildings or Class 2 / Class 3 Residential Buildings

In a Class 9c, Aged Care Building or Class 2 / Class 3 Residential Buildings, we find a wet pipe automatic fire sprinkler system installed and fitted with a flow switch as the primary alarm signalling device. In these scenarios there is no water-motor direct brigade alarm or alarm pressure switch fitted.

Where the building requires two or more automatic fire sprinkler systems due to its size or other requirements, then each automatic fire sprinkler system will be fitted with its own water flow switch.

Combined Hydrant / Fire Sprinkler Systems

The cost saving benefits of a Combined Hydrant / Fire Sprinkler System typically mean that these systems may not be fitted with a traditional sprinkler alarm valve.  In these systems the building is fitted with a combined hydrant / fire sprinkler system water supply.

On each floor of the building or in each fire zone a monitored sprinkler isolation (stop) valve is fitted along with a flow switch.  In this case, the water supply in the protected area may be isolated independently of the entire fire sprinkler system.

Under normal conditions when water flow is detected off the branch of combined main water supply serving the automatic fire sprinkler system an alarm signal is activated indicating;

1. water flow within the protected area; and
2. the operation of the automatic fire sprinkler system.

These systems are very common in buildings such as apartment buildings.

In each of the aforementioned Class 9c, Aged Care Buildings, Class 3 Residential Buildings or Combined Hydrant / Fire Sprinkler Systems there are always exceptions to the rule, and these descriptions are general in nature and actual system configurations and operation from one building to another may change.

In summary, an automatic fire sprinkler system is fitted with a flow switch to detect the flow of water for one or each of the following two reasons;

1. to detect the flow of water and identify the location of that water flow. That signal can then be used to provide local alarm annunciation and activate ancillary controls within the building. In this case the building will also be fitted with a water-motor alarm or a pressure switch to signal the fire brigade; or
2. to detect the flow of water for the primary purpose of activating a signal to the fire brigade and and activate ancillary controls within the building.

It can be difficult for a person who is not familiar with the various types of automatic fire sprinkler systems in a building to determine the function of their flow switches.

In these cases, it may be beneficial to clearly identify the operation of a flow switch in the building.  This can be done on the zone block diagram, with a label on the Fire Detection Control and Indicating Equipment ("FDCIE") or with a label on the flow switch.

One of the methods we employ is to use the background on the zone label on the FDCIE in a different colour with alarm signals that call the fire brigade.  We typically use YELLOW background with black text on the zone label to signify a non brigade calling alarm signal where a brigade calling signal is a WHITE background with black text.

It may come as a surprise to people not familiar with the operation of a fire detection and alarm system that not all fire alarm signals automatically call the fire brigade.  The most common of which are the following;

• a supply-air smoke detector; or
• a low-level (alert or fire 1) signal from an aspirating smoke detector.
• a white manual call point connected to an emergency warning system.

In these cases, the alarm signal is used for other purposes other than a brigade calling signal.

Firewize helps building owners with the routine servicing of their fire protection systems and equipment.  If your existing service provider is struggling to help you understand the operation of your fire and essential safety measures, then feel free to contact us and we can arrange a free no obligation site review and help you navigate the complex nature of fire systems maintenance and compliance.