1910.106 – Occupational Safety and Health Act

Flammable Liquids

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1910.106(a) – Definitions

 

1910.106(a)(2) – Atmospheric tank shall mean a storage tank which has been designed to operate at pressures from atmospheric through 0.5 psig

1910.106(a)(5) – Boiling point shall mean the boiling point of a liquid at a pressure of 14.7 pounds per square inch absolute (psia) (760 mm.). Where an accurate boiling point is unavailable for the material in question, or for mixtures which do not have a constant boiling point, for purposes of this section the 10 percent point of a distillation performed in accordance with the Standard Method of Test for Distillation of Petroleum Products, ASTM D-86-62, which is incorporated by reference as specified in § 1910.6, may be used as the boiling point of the liquid.

1910.106(a)(6) – Boil over shall mean the expulsion of crude oil (or certain other liquids) from a burning tank. The light fractions of the crude oil burn off producing a heat wave in the residue, which on reaching a water strata may result in the expulsion of a portion of the contents of the tank in the form of froth.

1910.106(a)(14) – Flashpoint means the minimum temperature at which a liquid gives off vapor within a test vessel in sufficient concentration to form an ignitable mixture with air near the surface of the liquid, and shall be determined as follows:

1910.106(a)(14)(i) – For a liquid which has a viscosity of less than 45 SUS at 100 °F (37.8 °C), does not contain suspended solids, and does not have a tendency to form a surface film while under test, the procedure specified in the Standard Method of Test for Flashpoint by Tag Closed Tester (ASTM D-56-70), which is incorporated by reference as specified in § 1910.6, or an equivalent test method as defined in Appendix B to § 1910.1200 – Physical Hazard Criteria, shall be used.

1910.106(a)(14)(ii) – For a liquid which has a viscosity of 45 SUS or more at 100 °F (37.8 °C), or contains suspended solids, or has a tendency to form a surface film while under test, the Standard Method of Test for Flashpoint by Pensky-Martens Closed Tester (ASTM D-93-71) or an equivalent method as defined by Appendix B to § 1910.1200 – Physical Hazard Criteria, shall be used except that the methods specified in Note 1 to section 1.1 of ASTM D-93-71 may be used for the respective materials specified in the Note. The preceding ASTM standard is incorporated by reference as specified in § 1910.6.

1910.106(a)(14)(iii) – For a liquid that is a mixture of compounds that have different volatilities and flashpoints, its flashpoint shall be determined by using the procedure specified in paragraph (a)(14)(i) or (ii) of this section on the liquid in the form it is shipped.

1910.106(a)(14)(iv) – Organic peroxides, which undergo autoaccelerating thermal decomposition, are excluded from any of the flashpoint determination methods specified in this subparagraph.

1910.106(a)(19) – Flammable liquid means any liquid having a flashpoint at or below 199.4 °F (93 °C). Flammable liquids are divided into four categories as follows:

1910.106(a)(19)(i) – Category 1 shall include liquids having flashpoints below 73.4 °F (23 °C) and having a boiling point at or below 95 °F (35 °C).

1910.106(a)(19)(ii) – Category 2 shall include liquids having flashpoints below 73.4 °F (23 °C) and having a boiling point above 95 °F (35 °C).

1910.106(a)(19)(iii) – Category 3 shall include liquids having flashpoints at or above 73.4 °F (23 °C) and at or below 140 °F (60 °C). When a Category 3 liquid with a flashpoint at or above 100 °F (37.8 °C) is heated for use to within 30 °F (16.7 °C) of its flashpoint, it shall be handled in accordance with the requirements for a Category 3 liquid with a flashpoint below 100 °F (37.8 °C).

1910.106(a)(19)(iv) – Category 4 shall include liquids having flashpoints above 140 °F (60 °C) and at or below 199.4 °F (93 °C). When a Category 4 flammable liquid is heated for use to within 30 °F (16.7 °C) of its flashpoint, it shall be handled in accordance with the requirements for a Category 3 liquid with a flashpoint at or above 100 °F (37.8 °C).

1910.106(a)(19)(v) – When liquid with a flashpoint greater than 199.4 °F (93 °C) is heated for use to within 30 °F (16.7 °C) of its flashpoint, it shall be handled in accordance with the requirements for a Category 4 flammable liquid.

1910.106(a)(21) – Low-pressure tank shall mean a storage tank which has been designed to operate at pressures above 0.5 psig but not more than 15 psig.

1910.106(a)(26) – Pressure vessel shall mean a storage tank or vessel which has been designed to operate at pressures above 15 psig.

1910.106(a)(33) – Barrel shall mean a volume of 42 U.S. gallons.

 

1910.106(b)(1)

TANK STORAGE – Design and Construction

 

1910.106(b)(1)(iii) –  Atmospheric Tanks

1910.106(b)(1)(iii)(b) – Tanks designed for underground service not exceeding 2,500 gallons capacity may be used aboveground.

1910.106(b)(1)(iii)(c) – Low-pressure tanks and pressure vessels may be used as atmospheric tanks.

1910.106(b)(1)(iii)(d) – Atmospheric tanks shall not be used for the storage of a flammable or combustible liquid at a temperature at or above its boiling point.

 

1910.106(b)(1)(iv) – Low Pressure Tanks

1910.106(b)(1)(iv)(a) – The normal operating pressure of the tank shall not exceed the design pressure of the tank.

1910.106(b)(1)(iv)(b) – Low-pressure tanks shall be built in accordance with acceptable standards of design. Low-pressure tanks may be built in accordance with the following consensus standards that are incorporated by reference as specified in Section 1910.106:

(1) American Petroleum Institute Standard No. 620. Recommended Rules for the Design and Construction of Large, Welded, Low-Pressure Storage Tanks, Third Edition, 1966.

(2) The principles of the Code for Unfired Pressure Vessels, Section VIII of the ASME Boiler and Pressure Vessels Code, 1968.

1910.106(b)(1)(iv)(c) – Atmospheric tanks built according to Underwriters’ Laboratories, Inc., requirements in subdivision (iii)(a) of and shall be limited to 2.5 psig under emergency venting conditions.

This paragraph may be used for operating pressures not exceeding 1 psig.

1910.106(b)(1)(iv)(d) – Pressure vessels may be used as low-pressure tanks.

 

1910.106(b)(2)

TANK STORAGE – Installation of outside aboveground tanks

 

1910.106(b)(2)(iv) –  Normal venting for aboveground tanks

1910.106(b)(2)(iv)(a) – Atmospheric storage tanks shall be adequately vented to prevent the development of vacuum or pressure sufficient to distort the roof of a cone roof tank or exceeding the design pressure in the case of other atmospheric tanks, as a result of filling or emptying, and atmospheric temperature changes.

(1910.106(b)(2)(iv)(b) – Normal vents shall be sized either in accordance with: (1) The American Petroleum Institute Standard 2000 (1968), Venting Atmospheric and Low-Pressure Storage Tanks, which is incorporated by reference as specified in Section 1910.106; or (2) other accepted standard; or (3) shall be at least as large as the filling or withdrawal connection, whichever is larger but in no case less than 1 1/4″ nominal inside diameter.

(1910.106(b)(2)(iv)(c) – Low-pressure tanks and pressure vessels shall be adequately vented to prevent development of pressure or vacuum, as a result of filling or emptying and atmospheric temperature changes, from exceeding the design pressure of the tank or vessel. Protection shall also be provided to prevent overpressure from any pump discharging into the tank or vessel when the pump discharge pressure can exceed the design pressure of the tank or vessel.

(1910.106(b)(2)(iv)(d) – If any tank or pressure vessel has more than one fill or withdrawal connection and simultaneous filling or withdrawal can be made, the vent size shall be based on the maximum anticipated simultaneous flow.

(1910.106(b)(2)(iv)(e) – Unless the vent is designed to limit the internal pressure 2.5 psi. or less, the outlet of vents and vent drains shall be arranged to discharge in such a manner as to prevent localized overheating of any part of the tank in the event vapors from such vents are ignited.

(1910.106(b)(2)(iv)(f)

(1) – Tanks and pressure vessels storing Category 1 flammable liquids shall be equipped with venting devices which shall be normally closed except when venting to pressure or vacuum conditions. Tanks and pressure vessels storing Category 2 flammable liquids and Category 3 flammable liquids with a flashpoint below 100 °F (37.8 °C) shall be equipped with venting devices which shall be normally closed except when venting under pressure or vacuum conditions, or with approved flame arresters.

(2) Exemption: Tanks of 3,000 bbls (barrels). capacity or less containing crude petroleum in crude-producing areas and outside aboveground atmospheric tanks under 1,000 gallons capacity containing other than Category 1 flammable liquids may have open vents. (See paragraph (b)(2)(vi)(b) of this section.)

(1910.106(b)(2)(iv)(g) – Flame arresters or venting devices required in paragraph (b)(2)(iv)(f) of this section may be omitted for Category 2 flammable liquids and Category 3 flammable liquids with a flashpoint below 100 °F (37.8 °C) where conditions are such that their use may, in case of obstruction, result in tank damage.

 

1910.106(b)(2)(v) –  Emergency relief venting for fire exposure for aboveground tanks

1910.106(b)(2)(v)(a) –  Every aboveground storage tank shall have some form of construction or device that will relieve excessive internal pressure caused by exposure fires.

1910.106(b)(2)(v)(b) – In a vertical tank the construction referred to in subdivision (a) of this subdivision may take the form of a floating roof, lifter roof, a weak roof-to-shell seam, or other approved pressure relieving construction. The weak roof-to-shell seam shall be constructed to fail preferential to any other seam.

1910.106(b)(2)(v)(c) – Where entire dependence for emergency relief is placed upon pressure relieving devices, the total venting capacity of both normal and emergency vents shall be enough to prevent rupture of the shell or bottom of the tank if vertical, or of the shell or heads if horizontal. If unstable liquids are stored, the effects of heat or gas resulting from polymerization, decomposition, condensation, or self-reactivity shall be taken into account. The total capacity of both normal and emergency venting devices shall be not less than that derived from Table H-10 except as provided in subdivision (e) or (f) of this subdivision. Such device may be a self-closing manhole cover, or one using long bolts that permit the cover to lift under internal pressure, or an additional or larger relief valve or valves. The wetted area of the tank shall be calculated on the basis of 55 percent of the total exposed area of a sphere or spheroid, 75 percent of the total exposed area of a horizontal tank and the first 30′ above grade of the exposed shell area of a vertical tank.

 

TABLE H-10 – WETTED AREA VERSUS CUBIC FEET FREE AIR PER HOUR
(14.7 psia and 60°F.)

SQ. FT.	CFH	SQ. FT.	CFH	SQ. FT.	CFH
20	21100	200	211000	1000	524000
30	31600	250	239000	1200	557000
40	42100	300	265000	1400	587000
50	52700	350	288000	1600	614000
60	63200	400	312000	1800	639000
70	73700	500	354000	2000	662000
80	84200	600	392000	2400	704000
90	94800	700	428000	2800	742000
100	105000	800	462000	and over
120	126000	900	493000
140	147000	1000	524000
160	168000
180	190000
200	211000

NOTE: Interpolate for intermediate values.

1910.106(b)(2)(v)(d) – For tanks and storage vessels designed for pressure over 1 psig, the total rate of venting shall be determined in accordance with Table H-10, except that when the exposed wetted area of the surface is greater than 2,800 square feet, the total rate of venting shall be calculated by the following formula:

CFH   =  1.107A^0.82

Where: CFH= Venting requirement, in cubic feet of free air per hour.
A = Exposed wetted surface, in square feet.

NOTE: The foregoing formula is based on:

Q   =   21,000A^0.82

 

 

1910.106(b)(2)(v)(e) – The total emergency relief venting capacity for any specific stable liquid may be determined by the following formula:

CAPACITY   =  V x 1337 / L√M

Where:
V= Cubic  feet of free air per hour from Table H-10
L = Latent heat of vaporization of specific liquid in BTU per pound
M = Molecular weight of specific liquids

 

1910.106(b)(2)(v)(f) – The required airflow rate of subdivision (c) or (e) of this subdivision may be multiplied by the appropriate factor listed in the following schedule when protection is provided as indicated. Only one factor may be used for any one tank.

0.5   For drainage in accordance with subdivision (vii)(b) of this subparagraph for tanks over 200 square feet of wetted area

0.3   For approved water spray
0.3   For approved insulation
0.15   For approved water spray with approved insulation

1910.106(b)(2)(v)(g) – The outlet of all vents and vent drains on tanks equipped with emergency venting to permit pressures exceeding 2.5 psig shall be arranged to discharge in such a way as to prevent localized overheating of any part of the tank, in the event vapors from such vents are ignited.

(1910.106(b)(2)(v)(h) – Each commercial tank venting device shall have stamped on it the opening pressure, the pressure at which the valve reaches the full open position, and the flow capacity at the latter pressure, expressed in cubic feet per hour of air at 60°F. and at a pressure of 14.7 psia

1910.106(b)(2)(v)(i) – The flow capacity of tank venting devices 12″ and smaller in nominal pipe size shall be determined by actual test of each type and size of vent. These flow tests may be conducted by the manufacturer if certified by a qualified impartial observer, or may be conducted by an outside agency. The flow capacity of tank venting devices larger than 12″ nominal pipe size, including manhole covers with long bolts or equivalent, may be calculated provided that the opening pressure is actually measured, the rating pressure and corresponding free orifice area are stated, the word “calculated” appears on the nameplate, and the computation is based on a flow coefficient of 0.5 applied to the rated orifice area.

 

1910.106(b)(2)(vi) –  Vent piping for aboveground tanks

1910.106(b)(2)(vi)(a) – Vent piping shall be constructed in accordance with paragraph (c) of this section.

1910.106(b)(2)(vi)(b) – Where vent pipe outlets for tanks storing Category 1 or 2 flammable liquids, or Category 3 flammable liquids with a flashpoint below 100 °F (37.8 °C), are adjacent to buildings or public ways, they shall be located so that the vapors are released at a safe point outside of buildings and not less than 12 feet above the adjacent ground level. In order to aid their dispersion, vapors shall be discharged upward or horizontally away from closely adjacent walls. Vent outlets shall be located so that flammable vapors will not be trapped by eaves or other obstructions and shall be at least five feet from building openings.

1910.106(b)(2)(vi)(c) – When tank vent piping is manifolded, pipe sizes shall be such as to discharge, within the pressure limitations of the system, the vapors they may be required to handle when manifolded tanks are subject to the same fire exposure.

 

1910.106(b)(3)

TANK STORAGE – Installation of underground tanks

1910.106(b)(3)(iv)(a) – Location and arrangement of vents for Category 1 or 2 flammable liquids, or Category 3 flammable liquids with a flashpoint below 100 °F (37.8 °C). Vent pipes from tanks storing Category 1 or 2 flammable liquids, or Category 3 flammable liquids with a flashpoint below 100 °F (37.8 °C), shall be so located that the discharge point is outside of buildings, higher than the fill pipe opening, and not less than 12 feet above the adjacent ground level. Vent pipes shall discharge only upward in order to disperse vapors. Vent pipes 2 inches or less in nominal inside diameter shall not be obstructed by devices that will cause excessive back pressure. Vent pipe outlets shall be so located that flammable vapors will not enter building openings, or be trapped under eaves or other obstructions. If the vent pipe is less than 10 feet in length, or greater than 2 inches in nominal inside diameter, the outlet shall be provided with a vacuum and pressure relief device or there shall be an approved flame arrester located in the vent line at the outlet or within the approved distance from the outlet.

1910.106(b)(3)(iv)(b) –  Size of vents. Each tank shall be vented through piping adequate in size to prevent blow-back of vapor or liquid at the fill opening while the tank is being filled. Vent pipes shall be not less than 1 1/4″ nominal inside diameter.

1910.106(b)(3)(iv)(c) – Location and arrangement of vents for Category 3 flammable liquids with a flashpoint at or above 100 °F (37.8 °C) or Category 4 flammable liquids. Vent pipes from tanks storing Category 3 flammable liquids with a flashpoint at or above 100 °F (37.8 °C) or Category 4 flammable liquids shall terminate outside of the building and higher than the fill pipe opening. Vent outlets shall be above normal snow level. They may be fitted with return bends, coarse screens or other devices to minimize ingress of foreign material.

1910.106(b)(3)(iv)(d) – Vent piping shall be constructed in accordance with paragraph (c) of this section. Vent pipes shall be so laid as to drain toward the tank without sags or traps in which liquid can collect. They shall be located so that they will not be subjected to physical damage. The tank end of the vent pipe shall enter the tank through the top.

1910.106(b)(3)(iv)(e) – When tank vent piping is manifolded, pipe sizes shall be such as to discharge, within the pressure limitations of the system, the vapors they may be required to handle when manifolded tanks are filled simultaneously.

1910.106(b)(3)(v)(b) – Openings for manual gaging, if independent of the fill pipe, shall be provided with a liquid-tight cap or cover. If inside a building, each such opening shall be protected against liquid overflow and possible vapor release by means of a spring loaded check valve or other approved device.

 

 

 

1910.106(b)(4)

TANK STORAGE – Installation of tanks inside of buildings

1910.106(b)(4)(ii) – Vents for tanks inside of buildings shall be as provided in subparagraphs (2) (iv)(v) (vi)(b), and (3)(iv) of this paragraph, except that emergency venting by the use of weak roof seams on tanks shall not be permitted. Vents shall discharge vapors outside the buildings.

1910.106(b)(4)(iii) – Vent piping shall be constructed in accordance with paragraph (c) of this section.

1910.106(b)(4)(iv) – Tank openings other than vents
1910.106(b)(4)(iv)(a) – Connections for all tank openings shall be constructed in accordance with paragraph (c) of this subparagraph.

1910.106(b)(4)(iv)(b) –  Each connection to a tank inside of buildings through which liquid can normally flow shall be provided with an internal or an external valve located as close as practical to the shell of the tank. Such valves, when external, and their connections to the tank shall be of steel except when the chemical characteristics of the liquid stored are incompatible with steel. When materials other than steel are necessary, they shall be suitable for the pressures, structural stresses, and temperatures involved, including fire exposures.

1910.106(b)(4)(iv)(c) –  Flammable or combustible liquid tanks located inside of buildings, except in one-story buildings designed and protected for flammable or combustible liquid storage, shall be provided with an automatic-closing heat-actuated valve on each withdrawal connection below the liquid level, except for connections used for emergency disposal, to prevent continued flow in the event of fire in the vicinity of the tank. This function may be incorporated in the valve required in (b) of this subdivision, and if a separate valve, shall be located adjacent to the valve required in (b) of this subdivision.

1910.106(b)(4)(iv)(d) – Openings for manual gaging, if independent of the fill pipe (see (f) of this subdivision), shall be provided with a vaportight cap or cover. Each such opening shall be protected against liquid overflow and possible vapor release by means of a spring loaded check valve or other approved device.

1910.106(b)(6) – Sources of ignition – In locations where flammable vapors may be present, precautions shall be taken to prevent ignition by eliminating or controlling sources of ignition. Sources of ignition may include open flames, lightning, smoking, cutting and welding, hot surfaces, frictional heat, sparks (static, electrical, and mechanical), spontaneous ignition, chemical and physical-chemical reactions, and radiant heat.