You know what fire sprinklers are, but do you know how they work? Fire sprinklers are a crucial part of protecting lives and property during a fire emergency. Understanding how they work can help homeowners, project managers, and industry professionals make informed decisions. From how they are triggered to temperature ratings and effectiveness against different types of fires, we’ll explore the ins and outs of fire sprinklers.

First, let’s clear up a common misconception. Fire sprinklers are activated by heat, not smoke. When the heat from a fire reaches a specific temperature, typically around 155-165°F (68-74°C), a heat-sensitive element in the sprinkler head triggers. This releases water directly onto the fire area. This rapid response helps contain or extinguish the fire, preventing it from spreading.

Understanding the science behind fire sprinklers means understanding the components and how they work. This knowledge is the foundation for choosing the right system for your specific safety needs.

What Triggers Fire Sprinklers to Go Off?

Fire sprinklers work because they activate when they get hot. When a fire starts, the air right above it gets hot very quickly. This hot air rises and spreads out along the ceiling. When the air gets hot enough and reaches a sprinkler head, it sets off a chain reaction. The heat-sensitive element in the sprinkler head, often a glass bulb filled with a glycerin-based liquid, expands until it breaks, releasing water onto the fire.

This design ensures that sprinklers activate only in response to actual fires, avoiding false alarms that could occur if they were triggered by smoke alone. The design of these systems takes into account the dynamics of heat movement, ensuring that only the sprinkler heads directly affected by the fire will activate. This localized activation helps to control the fire effectively while minimizing water damage to the property.

Are Fire Sprinklers Activated by Smoke?

A lot of people think that fire sprinklers are set off by smoke. In fact, in the case of residential fire sprinklers and the vast majority of commercial fire sprinklers, fire sprinklers are set off by heat, not smoke. They have to reach a certain temperature before they go off. Smoke doesn’t have enough heat energy to set off the system. It’s an important distinction to keep in mind so you don’t have false alarms and you only set off the system when you have a real fire.

Speaking of smoke detectors, they are not designed to detect fire but to detect the presence of smoke. Typically, you have a smoke detector with an associated flow switch with the protected fire sprinkler system. It is the early warning and gives you time to evacuate. If the temperature of the fire gets high enough, the fire sprinkler system does its job. It turns on and puts the fire out at the critical level of heat.

What Temperature Do Fire Sprinklers Go Off?

The temperature at which fire sprinklers activate is important in their selection. Most common fire sprinklers activate at 155-165 degrees Fahrenheit(57 to 74 degrees Celsius). However, some have a different temperature depending on the fire sprinklers’ environment. For example, an environment where you have temperatures routinely over 165 degrees, such as a foundry, may use fire sprinklers rated for higher temperatures.

For example, with glass bulb sprinklers, different colors of glass bulbs show different activation temperatures.

Orange or Red(135°F or 155°F): Typically used in standard environments such as residential or office spaces.

Yellow or Green(175°F or 200°F): Suitable for areas with higher ambient temperatures.

Blue, Purple, or Black(250-300°F, 325-375°F or 400-475°F): Used in high-heat environments like industrial warehouses or manufacturing plants.

How Can I Know the Temperature Rating of a Fire Sprinkler?

For glass bulb sprinklers, it’s easy to determine the temperature rating by the color codings. Please refer to the below chart for details (from NFPA 13 standards).

• Orange: 135°F / 57°C
• Red: 155°F / 68°C
• Yellow: 175°F / 79°C
• Green: 200°F / 93°C
• Blue: 250-300°F / 121-149°C
• Purple: 325-375°F / 163-191°C
• Black: 400-475°F / 204-246°C
  
  

For fusible alloy sprinklers, you can also tell the temperature rating range by checking the color on the sprinklers. Please also refer to the below chart for the color codings for fusible links(from NFPA 13 standards). Note that the color codings for glass bulbs and fusible links are different, so don’t mix them up.

• Uncolored or black: 135-170°F / 57-77°C
• White: 175-225°F / 79-107°C
• Blue: 250-300°F / 121-149°C
• Red: 325-375°F / 163-191°C
• Green: 400-475°F / 204-246°C
  
  

If you have a sprinkler in your hand, the easiest way to tell is to look at the markings on the sprinkler’s deflector plate. The working temperature is usually marked there.

Also, each type of sprinkler head has a specification sheet from the manufacturer that tells you the temperature rating, the water discharge rate, and the area it covers. You need to look at the specifications and consider the conditions where you are going to install the sprinklers. The temperature in the building, the potential fire hazards, and the layout of the building all affect which temperature rating you need for your sprinkler system.

What is the Science Behind Fire Sprinklers?

Fire sprinklers work on simple principles that have been proven effective over the years. A fire sprinkler system consists of a water supply, a network of pipes, a control valve, a waterflow alarm and sprinkler heads. The pipes are filled with water under pressure. Each sprinkler head contains a heat-sensitive element that blocks water flow. When exposed to heat from a fire, this element breaks or melts, allowing water to discharge.

The basic components of a sprinkler head include:

• Frame: The support structure of the sprinkler that holds everything together and connects all the pieces so the sprinkler works.
• Heat-sensitive Element: a) A glass bulb filled with a liquid that expands when heated; b) fusible links with a fusible alloy that melts when heated.
• Deflector: A plate that disperses water evenly over a designated area.
• Seal assembly: A plug that prevents water flow until the heat-sensitive element triggers.

Sprinklers are spaced to ensure that they cover the maximum possible area. The water from the sprinkler head forms a spray pattern designed to extinguish the fire or at least control its spread until the fire department arrives.

Do Sprinklers Put Out All Types of Fires?

Fire sprinklers are very effective at controlling or extinguishing many types of fires, including those caused by:

• Combustible materials such as wood, paper, and textiles.
• Flammable liquids such as gasoline or alcohol.
• Electrical equipment fires provided that the water does not come into direct contact with live electrical components.

But they are not effective against fires involving certain hazardous materials, such as certain chemicals or metals, which require specialized fire suppression methods. Also, in very large fires where multiple sprinklers activate, the water pressure may drop, reducing the system’s effectiveness.

Fire sprinkler systems are designed primarily for ordinary combustible fires (Class A), flammable liquids (Class B), and electrical fires (Class C). They are not intended for use against fires involving flammable metals (Class D) or cooking oils and fats (Class K). 

Considerations When Choosing Fire Sprinklers for Your Project

When you pick out fire sprinklers, there are several critical factors you need to think about to make sure you make the right choice.

• Thread Size: basically 1/2’’-DN15, 3/4’’-DN20 and 1’’-DN25, which must match the piping system it will be installed on.
  
  

• K-Factor: This number indicates how much water the sprinkler head releases or the size of the discharge orifice. The most commonly used in projects are K5.6/K80 and K8.0/K115. 
  
  

• Thermal Sensitivity: This refers to how quickly and accurately a sprinkler responds to heat. Typically, there are two types: fast response [with an RTI of 50 (meters-seconds)^1/2 or less] and standard response [an RTI of 80 (meters-seconds) ^1/2 or more].
  
  

• Temperature Rating: This is the temperature at which the sprinkler head turns on, typically 135°F / 57°C, 155°F / 68°C, 165°F / 74°C are most commonly used.
  
  

• Installation Orientation: Sprinklers are designed to be installed in a specific orientation, including upright, pendent, sidewall, concealed, recessed and flush.
  
  

• Certification: You need to check the specific certification requirements for your project based on the fire codes in your area. The certifications for fire sprinklers that are generally recognized in the international market are UL and FM. In some markets, such as China, you still need CCCF certification even if you already get UL and FM for the sprinklers.
  
  

• Others: If there are any special requirements for fire sprinklers, you need to find out about them ahead of time. For example, if you are using dry sprinklers, the length of the tube is completely custom based on the actual situation of the project, so you need to know that in advance.
  
  

In conclusion, understanding how fire sprinklers work is critical for anyone involved in fire safety. Fire sprinkler systems are a critical part of modern fire protection, and the right system can mean the difference between a minor incident and a major disaster. If you invest in the right fire sprinkler system and maintain it properly, you can provide a higher level of safety and peace of mind for the people who will be in the building and the person who owns the building.