Detector Response Time Calculator

Calculate heat detector and sprinkler response time using RTI and ceiling jet theory.

Input Parameters

Results

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Time Constant
sec
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Activation Time
sec
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Activation Time
min
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RTI Classification
Note: RTI characterizes how quickly a thermal element responds to temperature changes. Lower RTI = faster response. NFPA 72 and NFPA 13 use RTI for detector and sprinkler activation modeling. Quick-response elements have RTI <= 28 (m-s)^0.5.

Reference

Time Constant: tau = RTI / sqrt(U_jet) Activation Time: t = -tau x ln((T_jet - T_act) / (T_jet - T_amb)) RTI Classes: QR (Quick Response): RTI <= 28 (m-s)^0.5 Special: 28 < RTI <= 50 SR (Standard): 50 < RTI <= 80 Slow: RTI > 80 Based on first-order lumped mass heat transfer model.