As per NFPA 33, 2007 edition
9.1* General.
Spray areas, which include by definition any associated exhaust plenums and exhaust ductwork, any particulate filters, any solvent concentrator units, any recirculation air supply units, and mixing rooms, shall be protected with an approved automatic fire protection system.
9.4.5 The sprinkler system shall be controlled by a separate, listed indicating valve(s), operable from floor level.
9.4.6* Sprinkler systems protecting stacks or ducts shall meet all of the following requirements:
(1) Sprinklers shall be spaced no more than 3.7 m (12 ft) apart.
(2) If exhaust ducts are manifolded, a sprinkler shall be located in the manifold at the junction of each exhaust duct with the manifold.
(3) Sprinklers shall provide a minimum flow of 114 L/min (30 gpm) per head at a minimum of 1 bar (15 psi) pressure.
(4) Sprinklers shall be ordinary temperature rated, unless required to be higher due to operating temperatures measured in the ducts, in which case the operating temperature shall be at least 28°C (50°F) above the inside temperature of the duct.
9.4.6.1 Stacks and exhaust ducts shall be provided with access openings for inspection and cleaning of sprinklers.
9.4.6.2 Sprinkler systems protecting stacks and ducts that are subject to freezing shall be of a nonfreezing type or be a manually controlled open-head system.
9.4.7 Sprinklers shall be protected against overspray residue, either by location or covering, so that they will operate quickly in event of fire.
9.4.7.1 Sprinklers shall be permitted to be covered only by cellophane bags having a thickness of 0.08 mm (0.003 in.) or less or by thin paper bags. These coverings shall be replaced frequently so that heavy deposits of residue do not accumulate.
9.4.7.2 Sprinklers that have been painted or coated by overspray or residues shall be replaced with new sprinklers.
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