Emergency Lighting Duration After a Battery Swap
A three-storey office has a central battery emergency lighting system serving escape routes and a plant room. During a routine monthly test, several luminaires on the second floor failed to light, and the rest ran for only 45 minutes before dimming. The battery set is rated for 3 hours and is four years into a design life of five. A contractor replaces the battery set and restores the failed luminaires, then declares the system compliant on the basis of a 90-minute run test. The building has no record of the last full-duration test. The fire authority has asked for evidence before renewing the occupancy certificate.
1. Assess whether the contractor's 90-minute test is sufficient evidence of compliance, and explain what the earlier 45-minute result indicates.
Read the worked answer
A 90-minute run does not demonstrate compliance with a 3-hour design duration. The test must run for the full rated duration, because the purpose is to show the system will last the escape time plus margin under real conditions, including the load of all connected luminaires. A 90-minute pass only proves the system lasts half its design duration; the remaining 90 minutes are untested, and a battery that fades after 90 minutes would still pass.
The earlier 45-minute result is significant. It shows the battery set was already degraded before replacement, which is consistent with a four-year-old set approaching end of life, but it also raises the question of whether the load was correct. If luminaires had been added or the wiring altered, the battery may have been discharging into a larger load than designed, shortening runtime. Replacing the battery without checking the connected load and the charging arrangement could reproduce the fault.
The contractor's declaration is therefore not adequate evidence for the fire authority. A full-duration test of the new set, with all luminaires connected and the normal supply isolated, is required, together with a record of the connected load and the charger's performance.
2. List the checks and records you would require before the occupancy certificate is renewed.
Read the worked answer
Require a full-duration discharge test of the new battery set with the normal supply isolated, all escape-route and plant-room luminaires connected, and a logged result showing the system still meeting its illuminance requirement at the end of the rated duration. Record the start and end times, the battery voltage or current during the test, and the identity of the person who witnessed it.
Check the connected load against the battery's design rating, and confirm no luminaires have been added since the original design without recalculating the duration. Verify the charger is operating correctly and can recharge the set within the manufacturer's stated time, and confirm the charger's fault alarm is working and monitored.
Check that the monthly and annual test records exist and are complete; the absence of a full-duration test record is itself a finding. Confirm the failed luminaires were repaired and are now included in the test. Require a written test certificate and a schedule for the next full-duration test, and confirm the fire authority's specific evidence requirements are met before the certificate is renewed.