1910.94(c)(6) Velocity and Air Flow Requirements

Except where a spray booth has an adequate air replacement system, the velocity of air into all openings of a spray booth shall be not less than that specified in Table G-10 for the operating conditions specified. An adequate air replacement system is one which introduces replacement air upstream or above the object being sprayed and is so designed that the velocity of air in the booth cross section is not less than that specified in Table G-10 when measured upstream or above the object being sprayed.

TABLE G-10 - MINIMUM MAINTAINED VELOCITIES INTO SPRAY BOOTHS

Operating conditions for objects completely inside booth	Crossdraft, f.p.m.	Airflow velocities, f.p.m.
		Design	Range
Electrostatic and automatic air-less operation contained in booth without operator.	Negligible.	50 Large booth	50-75
Air-operated guns, manual or automatic	Up to 50	100 small booth 100 large booth	75-125 75-125
Air-operated guns, manual or automatic	Up to 100	150 small booth 150 large booth	125-175 125-175
		200 small booth	150-250

NOTES:

1. Attention is invited to the fact that the effectiveness of the spray booth is dependent upon the relationship of the depth of the booth to its height and width.
2. Crossdrafts can be eliminated through proper design and such design should be sought. Crossdrafts in excess of 100 fpm (feet per minute) should not be permitted.
3. Excessive air pressures result in loss of both efficiency and material waste in addition to creating a backlash that may carry overspray and fumes into adjacent work areas.
4. Booths should be designed with velocities shown in the column headed "Design. However, booths operating with velocities shown in the column headed "Range" are in compliance with this standard.

When an operator is in a booth downstream of the object being sprayed, an air supplied respirator or other type of respirator must be used by employees that has been approved by the NIOSH under 42 CFR part 84 for the material being sprayed.

Where downdraft booths are provided with doors, such doors shall be closed when spray painting.

In addition to the requirements in paragraph (c)(6)(i) of this section, the total air volume exhausted through a spray booth shall be such as to dilute solvent vapor to at least 25 percent of the lower explosive limit of the solvent being sprayed. An example of the method of calculating this volume is given below.

Example: To determine the lower explosive limits of the most common solvents used in spray finishing, see Table G-11. Column 1 gives the number of cubic feet of vapor per gallon of solvent and column 2 gives the lower explosive limit (LEL) in percentage by volume of air. Note that the quantity of solvent will be diminished by the quantity of solids and nonflammables contained in the finish.

To determine the volume of air in cubic feet necessary to dilute the vapor from 1 gallon of solvent to 25 percent of the lower explosive limit, apply the following formula:

Dilution volume required per gallon of solvent = 4 (100 - LEL) (cubic feet of vapor per gallon) divided by LEL

Using toluene as the solvent.

1. LEL of toluene from Table G-11, column 2, is 1.4 percent.
2. Cubic feet of vapor per gallon from Table G-11, column 1, is 30.4 cubic feet per gallon.
3. Dilution volume required =
   
   4 (100 - 1.4) 30.4 divided by 1.4 = 8,564 cubic feet.
4. To convert to cubic feet per minute of required ventilation, multiply the dilution volume required per gallon of solvent by the number of gallons of solvent evaporated per minute.

TABLE G-11 - LOWER EXPLOSIVE LIMIT OF SOME COMMONLY USED SOLVENTS

Solvent	Cubic feet per gallon of vapor of liquid at 70 deg. F.	Lower explosive limit in percent by volume of air at 70 deg. F.
	Column 1	Column 2
Acetone	44.0	2.6
Amyl Acetate (iso)	21.6	(1) 1.0
Amyl Alcohol (n)	29.6	1.2
Amyl Alcohol (iso)	29.6	1.2
Benzene	36.8	(1) 1.4
Butyl Acetate (n)	24.8	1.7
Butyl Alcohol (n)	35.2	1.4
Butyl Cellosolve	24.8	1.1
Cellosolve	33.6	1.8
Cellosolve Acetate	23.2	1.7
Cyclohexanone	31.2	(1) 1.1
1,1 Dichloroethylene	42.4	5.9
1,2 Dichloroethylene	42.4	9.7
Ethyl Acetate	32.8	2.5
Ethyl Alcohol	55.2	4.3
Ethyl Lactate	28.0	(1) 1.5
Methyl Acetate	40.0	3.1
Methyl Acetate	80.8	7.3
Methyl Cellosolve	40.8	2.5
Methyl Ethyl Ketone	36.0	1.8
Methyl n-Propyl Ketone	30.4	1.5
Naphtha (VM&P) (76 deg. Naphtha)	22.4	0.9
Naphtha (100 deg. Flash) Safety     Solvent - Stoddard Solvent	23.2	1.0
Propyl Acetate (n)	27.2	2.8
Propyl Acetate (iso)	28.0	1.1
Propyl Alcohol (n)	44.8	2.1
Propyl Alcohol (iso)	44.0	2.0
Toluene	30.4	1.4
Turpentine	20.8	0.8
Xylene (o)	26.4	1.0

Footnote(1) At 212 deg. F.