NFPA 262-1999 Standard Method of Tests for Flame Travel and Smoke of Wires and Cables for Use in Air-Handling Spaces.
2-2.5.2 The unit shall be secured to the exhaust end of the fire-test chamber. 2-2.6 Exhaust System. The exhaust system shall consist of the exhaust duct, smoke measurement system, exhaust duct damper, and a blower. 2-2.6.1* Exhaust Duct. The 16 in. ± 0.125 in. (406 mm ± 3 mm) diameter exhaust duct shall be constructed from stain- less steel and shall run 12 diameters horizontally in sufficient length downstream from the vent end of the rectangular-to- round transition, prior to location of instrumentation, to pro- vide for a fully developed exhaust gas flow. It shall extend a minimum of 28 ft (8.5 m) from the vent end of the exhaust transition section. The duct shall be insulated with at least 2 in. (51 mm) of high-temperature mineral composition material from the end of the exhaust transition piece to the photome- ter location. 2-2.6.2 Exhaust Duct Damper. A single blade duct volume control damper, for a nominal 16 in. (406 mm) diameter duct, shall be positioned in the exhaust duct 5.5 ft ± 0.5 ft (1.7 m ± 0.2 m), downstream of the smoke measurement system. The relative locations of the exhaust transition piece, exhaust duct, smoke measurement system and exhaust duct damper are shown in Figure 2-2.6.2. To maintain airflow control through- out each test run, the exhaust-duct damper shall be controlled by a closed-loop feedback system with respect to the air inlet draft gauge static pressure.
2-4 Fire-Test Chamber Airflow System. 2-4.1 An air intake, fitted with a vertically sliding shutter that extends the entire width of the test chamber, shall be provided at the fire end. The draft plate shall be positioned to provide an air- inlet port, as shown in Figure 2-2.1. 2-4.2 Movement of air throughout the exhaust duct shall be by induced draft. The draft-inducing system shall have a total draft capacity of at least 0.15 in. of water column (37 Pa) with the spec- imens in place, with the shutter at the fire end open to its normal position, and with the damper in the wide-open position. (See Sec- tion C–C in Figure 2-2.6.2.) A draft-gauge manometer to indicate static pressure shall be inserted through the top at the mid width of the tunnel, 1.0 in. ± 0.5 in. (25 mm ± 13 mm) below the ceiling, and 15.0 in. ± 0.5 in. (380 mm ± 13 mm) downstream of the air intake shutter as shown in Section C–C of Figure 2-2.6.2. 2-4.3 An automatic draft-regulator controller shall be mounted in the vent pipe downstream of the exhaust damper. Other man- ual, automatic, or special draft-regulation devices shall be permit- ted to be incorporated to maintain airflow control throughout each test run.NFPA 262 pdf download.