- Response Time Index ("RTI")
The Response Time Index (RTI) for an automatic fire sprinkler head measures the responsiveness (speed of activation) of the sprinkler when exposed to a fire. RTI, expressed in units of (m·s)1/2, is calculated based on the thermal sensitivity of the sprinkler head.
Different sprinkler types such as Quick Response (QR) and Standard Response (SR) vary in RTI values, with QR sprinklers having lower RTI values, indicating faster response times suitable for different fire hazard levels.
The formula for Response Time Index (RTI) is typically expressed as follows:
RTI Formula:
- RTI represents the Response Time Index.
- tr is the response time of the sprinkler in seconds.
The time it takes for the sprinkler head to activate when exposed to heat from a fire. - u is the velocity of the air in m/s.
The speed at which the hot gases move past the sprinkler head, influencing the heat transfer rate. - ΔTb is the temperature rise of the sprinkler bulb in °C.
The increase in temperature required to activate the sprinkler bulb. - ΔTg is the temperature rise of the gas (air) in °C.
The temperature difference between the surrounding hot gases and the sprinkler bulb. - C is the Conductivity Factor.
A factor that accounts for the thermal conductivity of the sprinkler head materials, affecting how quickly it heats up.
This formula is used to calculate the RTI, which is crucial in determining the thermal sensitivity and response time of fire sprinklers under specified conditions.