(1) Construction. Spray booths must be substantially constructed of steel, securely and rigidly supported, or of concrete or masonry except that aluminum or other substantial noncombustible material may be used for intermittent or low volume spraying. Spray booths must be designed to sweep air currents toward the exhaust outlet.

(2) Interiors. The interior surfaces of spray booths must be smooth and continuous without edges and otherwise designed to prevent pocketing of residues and facilitate cleaning and washing without injury.

(3) Floors. You must cover the floor surface of a spray booth and operator's working area, if combustible, with noncombustible material of such character as to facilitate the safe cleaning and removal of residues.

(4) Distribution or baffle plates. Distribution or baffle plates, if installed to promote an even flow of air through the booth or cause the deposit of overspray before it enters the exhaust duct, must be of noncombustible material and readily removable or accessible on both sides for cleaning. Such plates must not be located in exhaust ducts.

(5) Dry type overspray collectors—(Exhaust air filters). In conventional dry type spray booths, overspray dry filters or filter rolls, if installed, must conform to the following:

(a) You must design, install, and maintain the spraying operations except electrostatic spraying operations so that the average air velocity over the open face of the booth (or booth cross section during spraying operations) is not less than 100 linear feet per minute. Electrostatic spraying operations may be conducted with an air velocity over the open face of the booth of not less than 60 linear feet per minute, or more, depending on the volume of the finishing material being applied and its flammability and explosion characteristics. You must install visible gauges or audible alarm or pressure activated devices to indicate or ensure that the required air velocity is maintained. Dry spray booths equipped with a filter roll which is automatically advanced when the air velocity is reduced to that specified in this section should be arranged to cause shutdown of spraying operations if the filter roll fails to advance automatically. Maintenance procedures should be established to assure replacing filter pads before excessive restriction to airflow occurs. Filter pads should be inspected after each period of use and clogged filter pads discarded and replaced. You must inspect filter rolls to ensure proper replacement of filter media.

(b) You must immediately remove all discarded filter pads and filter rolls to a safe, well-detached location or placed in a water-filled metal container and disposed of at the close of the day's operation unless maintained completely in water.

(c) The location of filters in a spray booth must be so as to not reduce the effective booth enclosure of the articles being sprayed.

(d) You must protect space within the spray booth on the downstream and upstream sides of filters with an approved automatic sprinkler system meeting one of the following requirements:

(i) An automatic sprinkler system as defined in WAC 296-24-607; or

(ii) A fixed dry chemical extinguishing system as defined in WAC 296-24-622; or

(iii) A fixed carbon dioxide gaseous agent system as defined in WAC 296-24-623.

(e) You must not use filters or filter rolls when applying a spray material known to be highly susceptible to spontaneous heating and ignition.

(f) Clean filters or filter rolls must be noncombustible or of a type having a combustibility not in excess of Class 2 filters as listed by Underwriters' Laboratories, Inc. You must not alternately use filters and filter rolls for different types of coating materials, where the combination of materials may be conducive to spontaneous ignition. See also WAC 296-24-37013(6).

(6) Frontal area. Each spray booth having a frontal area larger than 9 square feet must have a metal deflector or curtain not less than 2 1/2 inches deep installed at the upper outer edge of the booth over the opening.

(7) Conveyors. Where conveyors are arranged to carry work into or out of spray booths, the openings therefor must be as small as practical.

(8) Separation of operations. You must separate each spray booth from other operations by not less than 3 feet, or by a greater distance, or by such partition or wall as to reduce the danger from juxtaposition of hazardous operations. See also WAC 296-24-37005(1).

(9) Cleaning. You must install spray booths so that all portions are readily accessible for cleaning. You must keep a clear space of not less than 3 feet on all sides free from storage or combustible construction.

(10) Illumination. When spraying areas are illuminated through glass panels or other transparent materials, you must use only fixed lighting units as a source of illumination. Panels must effectively isolate the spraying area from the area in which the lighting unit is located, and must be of a noncombustible material of such a nature or so protected that breakage will be unlikely. You must arrange panels so that normal accumulations of residue on the exposed surface of the panel will not be raised to a dangerous temperature by radiation or conduction from the source of illumination.