An automatic fire suppression system can be described as an extinguishing agent of fire designed under national fire protection association standard 13 (NFPA 13)
Different types of fire suppression systems
- Wet sprinkler system
- Dry pipe sprinkler system
- Foam fire sprinkler system
- Pre-action fire sprinkler system
- Deluge fire sprinkler system
1. Wet Sprinkler System
The primary aim of the Wet sprinkler system is to suppress the fire through discharging high-pressure water. The temperature is predefined in the system, as the temperature of the area increases than the set temperature, water goes out through the sprinkler system.
2. Dry Pipe Sprinkler System
Wet suppression systems are not applicable in cold countries like Antarctica, Canada, Greenland, etc due to the freezing of pipes. In those countries, dry pipe systems are implemented. These systems use pressurized air or nitrogen to fill the pipes.
In case of fire, the sprinklers will break and due to this air escapes through the pipe and the dry pipe valve opens. At this stage, water starts flowing through the open pipes to suppress the fire. Dry pipe installations are designed in unheated warehouses and attics.NFPA 13, NFPA 13R, and NFPA 13D cover sprinkler installation procedures in colder areas.
The dry pipe system uses an air compressor to fill the system with air. If the pipes are leaking the air compressor should run and due to this moisture content increases. The formation of ice indicates air leaks. It needs a proper investigation to find the leak source and to repair it further. NFPA 13 requires the valves and piping to be kept at 40-degree Fahrenheit or above. The heat source of the valve room should be permanently installed. This installation of piping, valves, and accessories require highly trained engineers, technicians, and supervisors. The hands-on experience was provided on most modern technologies. There are a lot of job vacancies in countries like Canada & Australia. There is a sufficient increase in the number of Indians trying to migrate to Canada.
The dry pipe valve consists of the following components
Clapper remains closed due to air pressure generated in the system. The air pressure in the system decreases when the sprinkler opens air, which creates a pressure difference between the upper and lower part of the clapper.
At this time the valve opens upward and water starts flowing through the clapper. The water flows in the area where air pressure is released.
In the dry pipe, the Clapper assembly acts as an interface between air and water. It will open only if there is any air loss. The area of the clapper is more on the airside than the waterside.
Low Body Drain Valve
When the clapper closes, a low body drain valve allows the air-side of the valve to be completely drained. The main drain valve lies below the clapper, clapper must be opened to drain the entire system.
The water supply pressure gauge and air pressure gauge are installed to monitor incoming water pressure and air pressure. These gauges also have a test valve with a plug.
There are two types of pressure switches installed on the dry pipe system. Air supply pressure switch monitors air loss and in case of air loss, the pressure switch sends a supervisory signal to the fire alarm control panel. The water pressure switch indicates water flow in the intermediate chamber or when the system is flooding.
Dry Pipe Valve Accelerator
As per NFPA 13, the time required to deliver water to the inspector’s test and drain is about 60 seconds. Some larger dry systems require a quick opening device to meet the NFPA standards. For systems up to 750-gallon capacity, one or two quick opening devices need to be installed. The basic type of quick opening device is accelerators and exhausters. The most common type is the accelerator. The accelerator can sense airdrop quickly and it can transfer the pressure to the intermediate chamber of the clapper. The accelerators are having more sensitive electronic components.
Air Maintenance Device
The automatic air maintenance device comprises valves, fittings, nipples, and actuators to automatically control the air pressure in the piping system. The air maintenance device feeds air into the piping system at the required volume and pressure from air sources like an air compressor.
3. Foam Fire Sprinkler System
The foam system uses a mixture of water and low concentric foam as an extinguishing agent in case of fire. The fire pump not only allows water but also a mixture of foam through the pipe, which aids to suppress the fire. A valve is used to connect foam systems and water supply pipes which depend on a heat detection system. These systems are used in high hazard areas like power plants, chemical storage areas, and warehouses.
Fixed foam systems are designed to operate under medium hazard and high hazard areas. Foam concentrate is supplied by the manufacturer which when mixed with water in correct proportions makes a foam solution. The most commonly used foam concentrates are aqueous film-forming foam (AFFF), alcohol-resistant aqueous film-forming foam (ARFFF), and high expansion foam.
The components of foam fire sprinkler systems are
A. Bladder Tank System
This system requires no additional power source, it needs a sufficient supply of water. The bladder tank is constructed using a carbon steel pressure vessel with a neoprene rubber pad that stores foam concentrate. The water supply inside the tank will collapse the bladder and helps in discharging the foam concentrate. The bladder tank consists of proportions, discharge devices, swing check valves, and hydraulic actuating ball valves. The bladder tank should be vertical and horizontal. Two types of proportioners in usage are variable range proportioner or conventional type.
B. Positive Displacement Foam Pump system
Positive displacement pumps are balanced pressure pumps. It consists of storage tanks, diesel or electric pumps, balancing valves, and electrical panels. Foam pumps are mainly positive displacement rotary pumps.
C. Foam Concentrate Proportioning Device
Foam concentrate proportioning devices consist of a positive displacement pump, an atmospheric tank, and adequate water supply. The atmospheric storage tank is made of polyethylene.
D. Foam Chambers
Foam chambers are foam discharging devices that also provide protection of storage tanks. The area of the foam chamber is the combination of a foam maker and a chamber connected with an air inlet. A removable orifice plate is located between flange inlet and pipe side flange. A vapour seal located in a foam chamber body prevents vapour from entering into the body.
- Pre-action Fire Sprinkler System
Pre-action fire sprinkler systems use the same principle of dry pipe systems. Here electrically operated valves i.e. pre-action valves are closed in the normal operating cycle. Valve operation is controlled by flame, heat, or smoke detection.
If there is an outbreak of fire, a pre-action valve helps to open the valve, thus water flows into the pipe and discharges water to suppress the fire. A double-locked interlock system installed in the pipe, which helps to pressurize air or nitrogen to the pipe. It also helps to check the leakages of the pipe. It prevents water from entering the system in case of false conditions.
Pre-action systems are installed in water sensitive areas like computer centers, libraries, and art museums. It gives full protection against unplanned discharge. There are single interlock systems and double interlock systems.
Single interlock systems – In case of any fire situation, the control panel inside the detection system activates the solenoid valve, making the pre-action valve open. The sprinkler systems are then filled with water.
Double interlock systems – it is a two-stage operation. Firstly the fire detection system needs to give a signal to open the valve which helps the pipes to fill with water. Secondly, it needs any of the sprinklers to open for discharging water to resist fire. Proper supervision is needed to monitor the works. A well-qualified supervisor should be monitoring the works.
5. Deluge Fire Sprinkler System
The Deluge fire system consists of air without any pressure in the pipes and the sprinkler heads are open in this. It consists of a deluge valve and it will be activated only after receiving signals from smoke detectors, heat detectors & optical flame detectors. It is used in high hazard areas like power plants & chemical plants. It can eliminate fire easily. The main advantage is that there will be no freezing in pipes when used in colder conditions. It is a quick response fire suppression system.
Disadvantages Of The Fire Sprinkler System
- Water will flow through the heads due to all heads being open.
- It requires a larger water reservoir to operate the system.
- It can damage sensitive equipment.
Advantages Of The Fire Sprinkler System
- It protects buildings that are spreading fire rapidly.
- This deluge system is less expensive
- It can be set off manually.
The document covers the different types of fire suppression systems and their applications. The fire suppression system is a basic defense mechanism against fire. The importance of fire fighting systems in industry is very valuable in saving so many lives and property. It also discusses the qualification and training needed to be undergone to work in Fire fighting systems.