Accident Prevention Manual for Business & Industry:

Engineering & Technology13th edition

National Safety Council

Compiled by Dr. S.D. Allen Iske, Associate Professor

University of Central Missouri

CHAPTER 12

FLAMMABLE AND COMBUSTIBLE LIQUIDS

Definitions As defined by NFPA 30, Flammable and Combustible

Liquid Code:

• Flammable Liquid is any liquid having a closed–cup flash point below 100°F, and having a vapor pressure not exceeding 40 psia at 100°F.

• Combustible Liquids are those with flash points at or

above 100°F but below 200°F.

Definitions (Cont.)• Flammable liquids—three classifications

• Class I liquids include those with flash points below 100°F.• Class IA includes those with flash points below 73°F and having a boiling

point below 100°F.• Class IB includes those with flash points below 73°F and having a boiling

point above 100°F.• Class IC includes those having flash points at or above 73°F and below

100°F.

• Combustible liquids—four classifications• Combustible liquids are those with flash points at or above 100°F.

• Class II includes those having flash points at or above 100°F and below 140°F.• Class III includes those having flash points of or above 140°F and are subdivided

as follows:• Class IIIA includes those with flash points at or above 140°F and below 200°F.• Class IIIB includes those with flash points at or above 200°F.

• Auto-ignition temperature: The minimum temperature at which a flammable gas-air or vapor-air mixture will ignite from its own heat source or a contacted heated source without the presence of an open spark or flame.

• Flammable limits: The minimum concentration below which propagation of flame does not occur on contact with a source of ignition is the lower flammable limit (LFL). The maximum proportion of vapor or gas in air above which propagation of flame does not occur is the upper flammable limit (UFL).

• Flammable range: Lies between the LFL and UFL, expressed as the percentage of vapor or gas in air by volume.

• Volatility: The tendency or ability of a liquid to vaporize.

Definitions (Cont.)

• Flash point: The minimum temperature at which a liquid gives off vapor concentrated enough to form an ignitable mixture with air near the surface of the liquid within a vessel. It is specified by the appropriate testing procedure and apparatus.

• Oxygen deficiency: An atmosphere having less than the percentage of oxygen found in normal air.

• Oxygen limits: For an explosion to occur, enough oxygen must be present along with a vapor concentration in the flammable range.

Definitions (Cont.)

Definitions (Cont.)• Propagation of flame: The spread of flame through the entire

volume of the flammable vapor-air mixture from a single source of ignition.

• Rate of diffusion: The tendency of gas or vapor to disperse into or mix with another gas or vapor, including air.

• Vapor pressure: The pressure exerted by a volatile liquid under any of the equilibrium conditions that may exist between the liquid and the vapor.

• Prevent dangerous mixtures• Avoid unintentionally mixing flammable and combustible

liquids. Mixing flammable or combustible liquids can lower the flash point of that liquid making it highly flammable.

• No smoking• In a building or area where flammable liquids

are stored, handled, or used, forbid personnel to smoke or carry matches, lighters or other spark-producing devices.

• Static electricity• Static electricity is generated by the contact and separation of

dissimilar materials. The principle hazards of static electricity are fire and explosion caused by spark discharges that contain enough energy to ignite flammable or explosive vapors, gasses, or dust particles.

General Safety Measures

• Bonding and Grounding• The purpose of bonding is to eliminate a difference in the static-

electrical-charge potential between two or more objects. • The purpose of grounding is to eliminate a potential difference

between an object and the ground.• When flammable liquids are

transferred from one container to another, provide a means of bonding between the two containersbefore pouring.

• An adequate ground will continuously discharge a charged, conductive body. As a safety measure, use a ground when any doubt exists concerning a situation.

General Safety Measures (Cont.)

• Electrical equipment• When flammable vapors exist, electricity becomes an ignition

source if the proper type of electrical equipment for these atmospheres either has not been installed or has not been maintained. Consult NFPA (National Fire Protection Association) and NEC (National Electrical Codes) .

• Spark-resistant tools• The hazard of flammable vapors or gasses igniting from sparks

must be recognized. Use special tools to minimize the danger of sparks in hazardous locations.

General Safety Measures (Cont.)

• Flammable and combustible liquids create a health hazard when inhaled or when they come in contact with the skin. Intoxication and other acute or chronic conditions may result from breathing vapors or flammable liquids.

Health Hazards

Combustible-Gas Indicators

• Unless tests prove otherwise, assume that flammable vapors and toxic mixtures are present in all tanks that have contained or have been exposed at any time to flammable and combustible liquids.

• Use approved chemical analytical methods to test for toxic substances.

• Allow only experienced operators to use a combustible-gas indicator.

• Safety procedures are required for tank cars and tank trucks used to transport flammable and combustible liquids.

• Refer to Association of American Railroads (AAR) and U.S. Department of Transportation (DOT) standards and codes.

• Only trained workers should load or unload tank cars containing flammable or combustible liquids.

• Do not load or unload cars before ensuring that no exposed lights, fires, or other sources of ignition are in the area.

• Closely check invoices and shipping papers on incoming tank cars to make certain they match the actual numbers on the tank car.

Loading and Unloading Tank Cars

Loading and Unloading Tank Cars (Cont.)

• Fire safety:• Ensure that no exposed lights, fires, or other sources of ignition are

in the area prior to loading or unloading cars.• Stop loading and unloading during electrical storms.• Know and execute safety procedures for handling fires.

• Personnel safety:• Only trained employees should load or unload cars.• Understand danger of fires, explosion, asphyxiation, and toxic

effects from exposure to vapors. Fall protection as required.• Set operational procedures for safety.

Loading and Unloading Tank Cars (Cont.)

• Environmental Protection• Use approved containers under any leaks to prevent contamination

and product loss.• Limit quantities of flammable liquids exposed to atmosphere and

released to ground.• Prepare for spills and emergency responses and compliance to

regulations.• Avoid spills and overflows.• Drivers must protect traffic and property.

Loading and Unloading Tank Cars (Cont.)

• Electrical considerations• Provide approved electrical equipment on tank cars. • Bound, ground, and insulate a tank car’s siding from the main rail

line for protection from stray electrical currents.

• Spotting cars• Use a car mover when it is necessary to spot a car by hand.

• Inspection• The company receiving or shipping a tank car should make a

general visual inspection of the unit and report any obvious defects to the carrier.

Loading and Unloading Tank Cars (Cont.)

• Relieving pressure• Relieve the tank car of interior pressure before removing the

domed manhole cover or the outlet valve cap. Raise the safety valves and open the air valve a small amount at a time.

• Removing covers• Loosen a screw-type dome cover by using a bar placed between

the lug and the knob on the cover’s top. Make two complete turns to expose the ½ in. vent holes in the threaded portion of the dome cover. Keep clear of vapors by standing upwind, out of vapor accumulation.

• Chemical and physical layout of the unloading area may require appropriate respiratory protection—SCBA or Air-Supplied Respirator.

Loading and Unloading Tank Cars (Cont.)

• Connections• Ensure integrity of the outlet valves• Examine the outlet chamber for cracks before unloading.• Use safe procedures to modify for temperature changes at valves.• Worker should be in attendance during the entire loading or

unloading process.• Use proper venting and vapor recovery units.

• Placards and shipping papers• Follow proper U.S. DOT or counterpart regulatory guidelines for

using placards and shipping papers.

• Inspection• See that trucks are kept in good repair and inspected daily.

Place special emphasis on the condition of lights, brakes, horns, rearview mirrors, bonding straps, tires, steering, and motors.

• Smoking• Prohibit smoking by truck drivers and anyone who helps driving,

loading or unloading, or attending to their unit.• Provide each tank vehicle with at least one fire extinguisher,

each having at least a 10 B, C rating.

• Spotting trucks• When a tank truck is being loaded or unloaded, see that the

brakes are set, the engine stopped, the lights are turned off, and the bonding connection is made before the dome cover is opened for inspection.

Loading and Unloading Tank Trucks

• Unloading and loading connections• Trucks with motor-driven pumps should be shut off before loading

lines are connected or disconnected. • Drivers must remain at the tank controls (within 25 ft).

• Leaks• Avoid spills or overflows. If they do occur, immediately stop

loading, shut off the valves, and clean up the overflow before resuming loading. Trap the liquid in containers, in an earthen or sand-diked area, or in depression or pit, if possible.

• Fires• In the event of a tank-truck fire during loading or unloading, shut

off the fuel supply to or from the truck if possible. Remove the spout from the tank truck. To put out the fire use CO2, foam, or dry chemical extinguishers.

Loading and Unloading Tank Trucks (Cont.)

• Keep or store Class I and Class II liquids within approved containers in buildings used for public assembly, such as schools, churches, or theaters.

• Keep the containers in a storage cabinet or a storage room that does not open to a public portion of the building.

• Limit the quantities stored in such locations (NFPA 30).• Do not store containers where they will obstruct exits,

stairways, or other areas used to safely leave the building. • Never store containers near stoves or heated pipes or

expose them to sunlight or other sources of heat.• Do not store flammable or combustible liquids in open

containers.

Nonbulk Storage

.

Nonbulk Storage (Cont.)• Inside storage and mixing rooms

• Flammable or combustible liquids in approved, sealed containers present a potential, rather than an active, hazard.

• Isolate inside storage rooms as much as possible.• Locate at or above grade along an exterior wall.• NFPA 30 specifies architectural and mechanical requirements.

• Inside storage cabinets• Codes most stringent for Class 1A liquids; some limit operations to 10

gallons stored outside cabinets per control area.• Cabinets should be made of metal or wood and conform to ANSI

standards and NFPA 30.• According to NFPA 30, no more than 120 gallons of Class I, Class II,

and Class IIIA liquids may be stored in an approved storage cabinet for flammable liquids. • Of this total, not more than 60 gallons may be of Class I and Class II liquids.• No more than 3 cabinets may be in a single control area.

• Label required: FLAMMABLE – KEEP FIRE AWAY!

Non-bulk Storage (Cont.)

• Outside storage lockers• If space permits, construct storage areas for flammable liquids as

separate buildings set aside from main facility.• Construct similar to inside storage rooms.• Approved pre-fabricated lockers may be used.• Consult local regulations for location and use of outdoor storage

lockers.

Cleaning Small Tanks• Work on a container that held flammable or combustible

liquids should be supervised by trained individual.• Take special precautions for containers that held reactive

compounds (perchlorates, peroxides, nitrates, etc.)• Note that container may have sufficient oxygen level for

combustion.• See SDS for cleaning procedures.

• Clean in an approved area with ample ventilation.• When possible, clean outdoors and away from ignition

source.• Steaming, hot chemical washes, water filling, and use of

inert gas are common methods for cleaning and vapor removal.

• Return unused, uncontaminated flammable liquids to the vendor, salvage them for resale, or use them in some other approved way.

• Mixture of clean flammable liquids sometimes need to be separated before they are usable.

• If recycling or recovery of flammable liquids is not feasible, give them to a licensed disposal contractor.

Disposal of Flammable Liquids

Regulatory Issues• Receiving, storing, handling, and using flammable and

combustible liquids requires precautions and safe practices. Be sure to consult:• Regulations• Local codes• Fire underwriters• NFPA• DOT• OSHA standards• Trade associations• Specific handbooks

Bulk Storage: Installation and Maintenance

• Tank construction• All aspects of tanks should conform to NFPA 30A.

• Store bulk quantities of Class I in underground tanks or outside buildings.

• Vents• Provide storage tanks with vents per NFPA 30.

• They should also be higher than the fill pipe opening and not less than 12 ft above the adjacent ground level.

• Discharge vertically and so no vapors can enter building. Flame arrestors.

• Dikes• Flow of flammable /combustible liquid can have serious

consequences because of topography or neighboring property.• In these cases, install a curb, dike, or wall around a tank or group the tanks.

• Pumps• Locate flammable liquid transfer pumps outside the buildings and

diked areas whenever possible.• Use fire resistant construction in buildings that house equipment for transferring

flammable liquids.• Good Housekeeping is essential for good safety practices.

Bulk Storage• Gauging

• Allows operators to keep track of liquid levels in tanks. • If a tank requires manual gauging and a walkway is not provided, arrange

a way for employees to measure the contents of storage tanks so that they need not walk across the tank roof.

• Protect employees and provide early detection of releases.

• Underground Tanks• When an underground tank is subject to heavy traffic over it, protect the

tank with at least 3 ft. of earth cover, 18 in. of tamped earth plus 6 in. of reinforced concrete, or 18 in. of tamped earth plus 8 in. of asphalt concrete.

• Specific design and installation requirements, firm foundations, surrounding “jackets” of non-corrosive, inert materials to protect from leaks.

• Aboveground tanks• Refer to NFPA 30, when storing aboveground tanks. NFPA sets minimum

distances from property lines, public ways, and nearby buildings.• For different types of flammable and combustible liquids there are different

boundaries set. See Tables 12-A, 12-B and 12-C.

Bulk Storage• Spill control

• Release of flammable or combustible liquids may have serious consequences due to topography and property.

• Use curb, wall or dike around a tank or group of tanks.• Structure should have capacity of the single largest container.• Equip areas with drain systems and control valves to prevent

leakage into water supplies, public sewers or storm drains.

• Tank fires and their control• Prevention is the best way to reduce the risk of fires in storage

tanks.• Provide tanks containing flammable liquids with a roof that floats

upon the surface of the liquid—an internal or external open-top floating roof.• Such a roof greatly reduces the opportunity for vapors to accumulate within

the flammable range

Cleaning Tanks• General precautions

• Confined-space entry procedures, appropriate training• Clean tanks and vessels that have contained flammable and combustible

liquids before inspections, repairs, entry by personnel, or changes of product.• An industrial plant lacking proper equipment and should consult supplier of

flammable or combustible liquids.

• Protective equipment• Workers who are cleaning tanks should wear proper and appropriate PPE.• A worker entering a tank and spending an extended time inside must wear a

supplied-air, full-face mask and a safety harness with a lifeline for rescue.

• Proper procedures• A tank should be free of hazardous vapors and toxic materials before any

work is performed.• Be sure that employees engaged in tank cleaning know appropriate first aid

and CPR.• Have an attendant to monitor the worker’s behavior and know when to order

an evacuation.

1. Empty tank.2. Purge the tank of all flammable vapors using ventilation, displacement, and other means.3. Check atmosphere in tank to determine oxygen and flammable vapor levels.4. Remove from the vicinity of the tank all sources of ignition.5. Obtain appropriate confined-space entry and hot-work permits.6. Disconnect and blank all products, steam, foam and similar lines.7. Lock out all electrical equipment and use only lighting approved for specific atmosphere.8. Undo all but four bolts on one manway and slowly open the remaining bolts.9. After all available product has been removed, the tank is ready for ventilation.10. Consult your supplier or refer to the appropriate manuals for advice on ventilating and

cleaning tanks.11. Bond steam lines and water wash nozzles to the tank.12. Ventilate or steam the tank.13. Do gas-hazard test to see if the tank has adequate oxygen and is free of any flammable

or toxic vapors.14. Have all personal protective equipment available.15. Test for oxygen and flammable content with a calibrated and adjusted oxygen monitor.16. When entering the tank, wear a fresh-air hose mask, air-supply tanks, and safety belts.17. Continue ventilation for the duration of the work in the tank.18. If inert gas has been used for freeing gas, check for oxygen deficiency.

Cleaning Storage Tanks

Abandonment of Tanks• Authorities require removal of tanks at the end of their

useful life and generally will not accept abandoning tanks in place.

• Thoroughly clean obsolete tanks to remove flammable vapors.

• Dismantle and remove them from the premises according to the U.S. EPA underground storage tank regulations.

• If temporarily out of service, cap and secure fill lines, gauge openings, and pump suction lines to reduce tampering and accidental filling. Leave vent lines open.

Common Uses of Flammable and Combustible Liquids

• Dip tanks• Present a severe fire and explosion hazard—large exposed surface of flammable and

combustible liquids leads to increased risk of fire.• Conduct dipping operations above grade in a detached, one-story building of non-

combustible construction, or in separate one-story section.• Use room as large as possible to allow vapor dilution and reduced vapor accumulation.• Use mechanical ventilation that directs fresh air over vapor area, past point of

operation, and then to safe outside location.• Fire codes require interlock in case of ventilation failure.

• Japanning and drying ovens• Ovens used for evaporating varnish, Japan enamel, and other flammable and

combustible liquids can present serious fire and explosion hazards.• Provide ample ventilation and explosion venting for these ovens.• Provide ovens with proper fire-extinguishing equipment and interlocks to shut down

process in case of fire.

• Oil burners• Oil and diesel can be used as fuel in heating applications.• Use oil burners that are approved by a recognized testing

laboratory.• To prevent faulty ignition or accumulation of soot, use the correct

type of fuel oil, as recommended by the manufacturer.• Locate an industrial fuel oil supply tank outdoors and above

ground. Protect tank and piping to contain leaks and spills.

• Cleaning metal parts• Refined petroleum solvents are used for cleaning grease and oil

from metal parts where ordinary ventilation is provided and the area is clear of sources of ignition.

Common Uses of Flammable and Combustible Liquids

• Internal-combustion engines• To prevent the accumulation of rubbish, oil or fuel, and rags around

industrial internal-combustion engines, practice good housekeeping.

• Spray booths• Conduct paint-spraying operations in detached buildings or away from

other operations, when possible.• Use approved spray rooms or booths with adequate ventilation.• Provide large spraying operation with automatic fire controls. Automatic

sprinklers or inert agents (CO2 ) systems are most effective.

• Liquefied petroleum gasses• Gasses that liquefy under moderate pressure but convert to a gaseous

state upon relief of the pressure. (e.g., propane, butane, propylene, and butylenes)

• LPG vapors presents similar hazard to any flammable gas. LPG vapor is heavier than air; collects in low areas and requires ventilation.

• Use only experienced and reliable manufacturers and installers.

Common Uses of Flammable and Combustible Liquids