Sprinkler Response Time

Put desired value in the box or chose the pre-determined value by ticking one of the suggested options

Response Time Index (RTI)

√m∗√s

Response Time Index (RTI)

The thermal sensitivity of a sprinkler measures how quickly the thermal element operates. Perhaps the most common way of measuring thermal sensitivity is the response time index (RTI). Sprinklers are then categorized into fast or standard response based on their RTI. The RTI is typically determined by conducting a plunge test in which a sprinkler is placed (plunged) into a heated laminar airflow within a test oven. Then, the operating time of the sprinkler, the operating temperature of the sprinkler’s heat-responsive element, the air temperature of the test oven, the air velocity of the test oven, and the sprinkler’s conductivity factor are used to calculate the RTI. Additional factors impact the response such as the temperature rating of the sprinkler, sprinkler position, fire exposure, and radiation. The response time is expressed as a response time index (RTI), which typically has values between 35 m ½ s ½ and 250 m ½ s ½ , where a low value indicates a fast response.

Source: NFPA 13, Standard for the Installation of Sprinkler Systems, Edition 2022

Height of Ceiling, H

m

Ceiling Height

This is the height of the ceiling which is measured from the floor level.

Figure adopted from Dr Ronald L. Alpert’s presentation given on FIRESEAT 2011, Edinburgh, UK

Radial Distance, r

m

Radial Distance

This is the distance of the sprinkler from the center line of the smoke plume.

Figure adopted from Dr Ronald L. Alpert’s presentation given on FIRESEAT 2011, Edinburgh, UK

Fire Growth Rate, α

kW/s²

Fire Growth Rate

The fire growth rate (alpha) is a term used in fire engineering to describe the speed at which a fire increases in size or intensity over time. It is a measure of the rate of heat release from the fire, typically expressed in units of kW/m².

The alpha factor depends on various factors such as the fuel type, the ventilation conditions, and the geometry of the enclosure where the fire is burning. The following table has been adopted from BS 9999:2017 (Section 6.3)

Activation Temperature, T_act

℃

Sprinkler Activation Temperature

Looking closely at sprinklers with glass bulbs, it can be noticed that there are different colour bulbs. The colours identify the temperature rating of the sprinkler or in other word, the temperature at which sprinkler bulb activates and let the water flow. The temperature rating of the sprinkler selected needs to consider the maximum ambient ceiling temperature as well as the occupancy classification. If the maximum ambient ceiling temperature isn’t considered, it could result in accidental sprinkler operation since sprinklers are activated by heat. If the sprinkler does not have a glass bulb, then the frame arm, deflector or coating material will usually have some colour indicating the temperature rating. A range of sprinkler head operating temperature ratings is shown below.

Source:
BAFSA Information File, Sprinkler Heads; Issue 1; BIF No 8C, May 2010
NFPA 13, Standard for the Installation of Sprinkler Systems, Edition 2022

Ambience Temperature, T_amb

℃

Ambient Temperature

This is the room temperature at which the system implicates the study. The widely used temperature is used ranging from 18°C to 20°C in cold countries. However, this temperature can vary whether increasing or decreasing based on system specification or geographical locations.

Time Step

Timestep

This is the increment of time in the solver. For example, timestep = 1 means, the solver will iterate the equation with an increment of one second each time.

Total Duration

s

Duration of Fire

This is the value which indicates the duration of the fire that we want to simulate.

Activation time

Fire Size

Sprinkler Activation Time

The time at which sprinkler activates. For the simulation of the fire, is the point after which we can use the extinguishing factor or reduction factor.

Fire Size

The size of the fire at the time of sprinkler activation. This value is particularly helpful to estimate the maximum firesize in a compartment before the sprinkler activates.

Figure adopted from Dr Ronald L. Alpert’s presentation given on FIRESEAT 2011, Edinburgh, UK.

The correlations for jet temperatures and velocities were developed from data by R. L. Alpert

T_gas vs Time

Sprinkler Response Time

√m∗√s

m

m

kW/s²

℃

℃

s

Schematic of a Ceiling Jet Flow

Governing Equations

Visual Representation

Graphical Data