20 years.

According to NFPA 25, Standard for the Inspection, Testing, and Maintenance of Water-Based Fire Protection Systems, 2020 edition, fast response sprinklers are those that have a response time index (RTI) of 50 (m·s)^(1/2) or less.These sprinklers are designed toactivate faster than standard response sprinklers in the event of a fire, and they are typically used in light hazard, ordinary hazard, and residential occupancies1

NFPA 25 requires initial testing of representative samples of fast response sprinklers after 20 years from the date of manufacture, and subsequent testing every 10 years thereafter. The testing involves removing a minimum of four sprinklers or 1% of the total number of sprinklers per individual sprinkler sample, whichever is greater, and sending them to a recognized testing laboratory. The laboratory will perform a plunge test, which measures the time it takes for the sprinkler to operate when exposed to a specified air temperature.The test results will indicate whether the sprinklers meet the acceptance criteria or need to be replaced123

References:

NFPA 25: Standard for the Inspection, Testing, and Maintenance of Water-Based Fire Protection Systems1

Sprinkler System Inspections, Testing, and Maintenance Frequencies Explained | NFPA4

Sprinkler Testing on Quick Response Sprinklers: What You Need to Know2

NFPA 25 ITM Quick Reference Guide - hillgrp.com3