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Subchapter 7. General Industry Safety Orders
Group 16. Control of Hazardous Substances
Article 107. Dusts, Fumes, Mists, Vapors and Gases
§5154. Ventilation and Personal Protective Equipment Requirements for Open-Surface Tank Operations.
(a) General. This section applies to all operations involving the immersion of materials in liquids, or in the vapors of such liquids, for the purpose of cleaning or altering the surface character of the materials.
(1) Additional requirements for dipping and coating operations that use flammable liquids or liquids with flashpoints greater than 199.4o F (93o C).
Where flammable liquids are used in dipping and coating operations, the employer shall also comply with the requirements of Articles 136 and 137 and Sections 5143 and 5154, as applicable.
The employer shall comply with this subsection (a)(1) if:
• The flashpoint of the liquid is 199.4o F (93o C) or above
• The liquid is heated as part of the operation; or
• A heated object is placed in the liquid.
(b) Classification of Open-Surface Tank Operations.
The class is determined by two factors: hazard potential designated by a letter from A to D, inclusive, and the rate of gas, vapor, or mist evolution designated by a number from 1 to 4, inclusive.
(1) Table V-7 provides a classification system for the potential hazard of the vapor, gas, or mist originating from an open-surface tank, depending upon the toxicity or the flammability of the tank contents. The Table uses the respective concentration limit for an airborne contaminant (Section 5155) to define the health hazard and the flashpoint as the index of susceptibility to ignition; the higher of the two hazard ratings shall determine the appropriate classification. In evaluating the health hazard of a mixture of materials, other than organic solvents, the substance of lowest concentration limit (highest hazard) specified by Section 5155 shall determine the classification of the mixture, except where such substance constitutes an insignificant fraction of the mixture. The relative health hazard of a mixture of organic solvents is determined by the combined effects of solvent vapor concentrations in the operator's breathing zone. In absence of information to the contrary, the effects shall be considered as additive. The vapor concentrations may be measured individually, or calculated from the known composition of the liquid mixture by use of the vapor pressure value and the mole weight fraction value of each component in the mixture. The combined concentration limit is then calculated by using the following formula:
C is the concentration in parts per million of airborne solvent vapor from each component.
L is the time-weighted eight-hour exposure limit concentration in parts per million for each component. (See Section 5155 for TWA exposure limit values.)
Lm is the combined TWA exposure limit concentration for the airborne mixture of solvent vapors.
DETERMINATION OF HAZARD POTENTIAL
Time-Weighted Average Exposure Limit1
Gas and Vapor
1 As specified by Section 5155.
2 Closed-cup flashpoint; extensive flashpoint data are listed in the National Fire Protection Association Bulletin, NFPA 325M-1969.
(B) The classification index for the rate of evolution of a gas or vapor from an open-surface tank shall be determined from Table V-8.
DETERMINATION OF RATE OF GAS OR VAPOR EVOLUTION1
(Time for 100%
Fast (0-3 hours)
Medium (3-12 hours)
Slow (12-50 hours)
Nil (Over 50 hours)
1 In certain classes of equipment, specifically vapor degreasers, an internal condenser or vapor level thermostat is used to prevent the vapor from leaving the tank during normal operation. In such cases, rate of vapor evolution from the tank into the workroom is not dependent upon the factors listed in the Table, but rather upon abnormalities of operating procedure, such as carryout of vapors from excessively fast action, dragout of liquid by entrainment in parts, contamination of solvent by water and other materials, or improper heat balance. When operating procedure is excellent, effective rate of evolution may be taken as 4.
2 Relative evaporation times may be found in the Handbook of Organic Industrial Solvents, American Mutual Insurance Alliance (1972). The evaporation times given as rates in the Tables are the ratios of the time (in hours) required to evaporate the solvent, to the evaporation time (one hour) required for the same volume of ethyl ether. Evaporation times for solvents not listed in the handbook may be found in the article by A. K. Doolittle in Industrial and Engineering Chemistry, Anal. Ed.,Vol. 27, p. 1169 (1935).
(c) Control Requirements.
In all cases, the minimum control velocities shall conform to those listed in the following Table V-9.
MINIMUM CONTROL VELOCITIES IN FEET PER MINUTE
A-1 and A-2
Do not use.
Do not use.
A-3 (Note 2), B-1, B-2,
B-3, C-2, and D-1
A-4 (Note 2), C-3, and
B-4, C-4, D-3, and
General Room Ventilation Required.
1 See Table V-10 for computation of ventilation rate.
2 Do not use canopy hood for Hazard Potential A processes.
(d) Hood Classification.
A hood which projects over an entire tank and completely encloses at least two sides of the tank shall be considered to be an enclosing hood. A hood which does not project over the entire tank, and in which the direction of air movement is substantially horizontal, shall be considered to be a hood which ventilates laterally. Hoods that project over the entire tank, and which do not conform to the definition of enclosing hoods, shall be considered to be canopy hoods.
(e) Ventilation Rates.
(1) The minimum exhaust ventilation rate (cubic feet per minute) for canopy or enclosing hoods shall be not less than the product of the control velocity times the net area of all openings between or around the tank and the canopy or enclosure through which air can flow into the hood. If the estimated rate of vapor evolution (including steam or products of combustion) is equal to or greater than 10 percent of the exhaust volume required in Table V-10, the exhaust volume shall be increased in an equal amount.
(2) The minimum quantity of air in cubic feet per minute necessary to be laterally exhausted per square foot of tank area shall be determined from the following Table. The total quantity of air to be exhausted shall not be less than the product of the area of tank surface times the ventilation rate determined from Table V-10.
REQUIRED VENTILATION RATES IN CFM
Required Minimum Control
CubicFeet Per Minute Per Square Foot to Maintain
Velocity Feet Per Minute
Required Minimum Velocities at Following
(From Table V-9)
(The ratio of tank width to the tank length, W/L)1 2
Hood along side or two parallel sides of tank when one hood is against a wall or baffle (Note 2). Also for a manifold along tank centerline
Hood along one side or two parallel sides of free standing tank not against wall or baffle.
Notes: 1 It is not practicable to ventilate across the long dimension of a tank whose ratio W/L exceeds 2.0. It is undesirable to do so when W/L exceeds 1.0. For circular tanks with lateral exhaust aloing up to 1/2 the circumference, use W/L = 1.0: for over 1/2 the circumference use W/L = 0.5.
2 A baffle is defined as a vertical plate, the same length as the tank, which extends above the liquid level to a height at least equal to the width of the tank. If the exhaust hood is on the side of a tank against a building wall or close to it, it is adequately baffled.
3 Use W/2 as tank width in computing when manifold is along centerline, or when hoods are used on two parallel sides of a tank.
Note: Tank width (W) means the effective width over which the hood must pull air to operate (for example, where the hood face is set back from the edge of the tank, this set must be added in measuring tank width). The surface area of tanks can frequently be reduced, and better control obtained (particularly on conveyorized systems) by using covers extending from the upper edges of the slots toward the center of the tank.
(f) Push-Pull Systems Requirements. Push-pull systems shall not be used where there are obstructions between supply air streams and the exhaust slots which may interfere with the performance of the exhaust hood for more than a few seconds. When push-pull systems are used, they shall meet the following criteria:
(1) The exhaust air rate shall be at least 150 cubic feet per minute per square foot of tank surface area.
(2) The supply air rate shall not exceed 15 percent of the exhaust rate.
(3) The velocity in the effective control area shall be less than the exhaust slot velocity.
(4) The vertical height of the receiving exhaust hood shall not be less than one-quarter of the width of the tank.
(5) Methods of measuring and adjusting the supply air shall be provided and shall be fixed so that they will not be altered when satisfactory control has been achieved.
(g) Other Control Methods. In open-surface tank operations where control methods such as tank covers, foams, beads, chips, or other floating materials, surfactants, or any combination thereof, are used to prevent harmful exposure to mists and vapors, air monitoring at the operator's position shall be carried out at least quarterly to assure that allowable concentrations of airborne contaminants are not exceeded. A program shall be established to assure continued effectiveness of the control method. Records of the maintenance performed, sampling, and analyses shall be retained for at least five years.
(h) Vapor Degreasing Equipment.
(1) In vapor degreasing, the vapor level shall be maintained below the top edge of the tank by a distance at least equal to one-half the tank width, but need not exceed 36 inches. Control systems shall be designed and maintained to prevent decomposition of the solvent by overheating and to maintain the vapor-free zone specified.
(2) Tanks or machines of more than 4 square feet of surface area shall be equipped with suitable cleanout doors located near the bottom. These doors shall be designed and gasketed so there will be no leakage of solvent when they are closed.
(3) Where gas is used as a fuel for heating vapor degreasing tanks, the combustion chamber shall be of tight construction, except for such openings as exhaust flue, and those that are necessary for supplying air for combustion.Flues shall be of corrosion-resistant construction and shall discharge outdoors. Special precautions must be taken to prevent solvent vapors from entering the combustion air of this or any other heater when chlorinated or fluorinated hydrocarbons are used.
(i) Spray Cleaning and Degreasing. Wherever spraying or other mechanical means disperse a hazardous liquid above an open-surface tank, control must be provided for the airborne spray. Such operations shall be enclosed as completely as possible. The inward air velocity into the enclosure shall be sufficient to prevent the discharge of spray into the workroom. Mechanical baffles may be used to help prevent the discharge of spray.
(j) Personal Protection.
(1) All employees required to work in such a manner that any part of their person may be wet, splashed or contaminated with liquids other than water, shall be provided with appropriate protective clothing and equipment as prescribed in 8 CCR, Article 10. Such persons shall also be instructed as to hazards and safeguards of their respective jobs as required in Section 5194(h) and Section 5162(c).
(2) Whenever liquids or chemicals harmful on contact to the skin or eye tissues, or poisonous liquids or chemicals which can be absorbed through the skin, may splash or otherwise contact the employee's body, means of immediate rinse or dilution with clean water shall be provided, as required in Section 3400, Medical Services and First Aid and Section 5162, Emergency Eyewash and Shower Equipment. (Title 24, T8-5154(a), (b), (c), (d), (e), (f), (i))