2. Introduction
The two primary hazards
associated with flammable and
combustible liquids are explosion
and fire.
Safe handling and storage of
flammable liquids requires the use
of approved equipment and
practices per OSHA standards.
3. Fire Hazards
Fire hazards are associated with vapors from the
flammable liquid. In order for a fire to occur, the
following conditions must be met:
• Concentration of the vapor must be between the
upper and lower explosion limit.
• An oxidizing material must be present.
• Source of ignition must be present.
4. Definitions
Volatility = tendency or ability of a liquid to vaporize.
Vapor pressure = measure of a liquid’s volatility. A high vapor pressure
usually is an indication of a volatile liquid, or one that readily vaporizes.
Boiling point = temperature at which the vapor pressure equals atmospheric
pressure, such that the pressure of the atmosphere can no longer hold the liquid
in a liquid state and bubbles begin to form. Generally, low boiling point
indicates high vapor pressure (possibly, increased fire hazard).
Flashpoint = the least temperature at which vapors are ignited by an ignition
source and go out; no sustained combustion.
Flammable range = proportion of vapor to air mixture that is ignitable
(expressed in terms of percentage of vapor in air by volume).
Ignition Temperature = A temperature unique to various materials where they
will combust due to an open flame source.
Auto ignition temperature = minimum temperature at which a vapor-air
mixture will spontaneously ignite, without the necessity of a spark or flame.
Vapor density = measure of a vapor’s weight when compared to air (air
assigned value of 1). Denser vapors tend to sink to floor level, less dense
vapors tend to rise to ceiling level.
5. Flammable (Explosive) Limits/Flammable
(Explosive) Range
• The terms flammable and explosive are used interchangeably since
unconfined vapors mixed in air will burn while confined vapors will
produce an explosion.
• The minimum vapor concentration in air that, when ignited, will propagate
a flame is the lower flammable limit (LFL or LEL).
• The maximum vapor concentration in air that when ignited will propagate a
flame is the upper flammable or explosive limit (UFL or UEL).
6. Flammable Liquid
• A liquid having a flash point below 100°F (38°C) and a vapor pressure not
exceeding 40 psi at 100°F
• Flammable liquids are subdivided as follows:
• Class IA: Liquids with a flash point below 73°F (23°C) and a boiling point
below 100°F. Examples: acetaldehyde, butyne, chloropropylene, dimethyl
sulfide, ethyl chloride, ethyl ether.
• Class IB: Liquids with flash point below 73°F and a boiling point at or
above 100°F. Examples: acetone, benzene, carbon disulfide, ethyl alcohol,
ethyl acetate, gasoline, hexane, isopropanol, methanol, toluene.
• Class IC: Liquids with a flash point between 73°F and 100°F. Examples:
amyl alcohol, butyl alcohol, isobutyl alcohol, methyl isobutyl ketone,
styrene, turpentine, xylene.
7. Combustible Liquid
A liquid having a flash point above 100°F. Combustible liquids are subdivided
as follows:
• Class II: Liquids with a flash point at or above 100°F and below 140°F
(60°C). Examples: No. 1, 2 and 3 fuel oils, kerosene, and hexyl alcohol.
• Class IIIA: Liquids with a flash point at or above 140°F and below 200°F
(93°C). Examples: aniline, benzaldehyde, butyl cellosolve, nitrobenzene
and pine oil.
• Class IIIB: Liquids with a flash point at or above 200°F. Examples: animal
oils; ethylene glycol; glycerin; lubricating, quenching, and transformer oils;
triethanolamine; benzyl alcohol; hydraulic fluids and vegetable oils.
8. Good Plan Components
A good plan for safe use of flammable and combustible liquids
contains at least these components:
Control of ignition sources
Proper storage
Fire control
Safe handling
9. Take adequate precautions to prevent ignition of flammable vapors. Some sources
of ignition include:
• Open flames
• Smoking
• Static electricity
• Cutting and welding
• Hot surfaces
• Electrical and mechanical sparks
• Lightning
Sources of Ignition
10. • Generated when a fluid flows through a pipe or from an
opening into a tank.
• Main hazards are fire and explosion from sparks containing
enough energy to ignite flammable vapors.
• Bonding or grounding of flammable liquid containers is
necessary to prevent static electricity from causing a spark.
Static Electricity
11. • Physically connect two conductive
objects together with a bond wire to
eliminate a difference in static charge
potential between them.
• Must provide a bond wire between
containers during flammable liquid filling
operations, unless a metallic path
between them is otherwise present.
Bonding
12. • Eliminates a difference in static
charge potential between
conductive objects and ground.
• Bonding eliminates a difference in
potential between objects.
• Does not eliminate a difference in
potential between these objects &
earth.
• Unless one of the objects is
connected to earth with a ground
wire.
Grounding
13. Always provide adequate ventilation to reduce the
potential for ignition of flammable vapors.
Ventilation
15. Tanks and Storage Equipment
Storage of liquid materials is commonly accomplished in industrial plants by use of
cylindrical, spherical or rectangular tanks. These tanks may be constructed of
wood, concrete, or metal, with metal being the most common material of
construction.
The design of storage vessels involves consideration of details such as size and
number of openings, shape of heads, necessary temperature and pressure
controls and corrosive action of the content.
The necessary wall thickness for metal vessels is a function of:
1. The ultimate tensile strength or the yield point of the metal at the operating
temperature.
2. The operating pressure
While in the storage tanks, these products may settle out undesirable substances such
as;
a) Water
b) Emulsions
c) Dirt etc.
This undesirable substances can then be removed through draw-off devices. Products
may also be mixed, blended and treated in storage tanks effectively, using the
large capacity available in these tanks.
16. Tanks and Storage Equipment
General
1. The ultimate tensile strength or the yield point of the metal at the
operating temperature.
2. The operating pressure
3. The diameter of the tank
4. Joint or welding efficiency
5. Various codes are available which specify the conditions that must be
met for different vessels.
For safe storage of petroleum products, we have to consider the product properties
such as volatility (RVP, pour point, flash point and others before we start designing
and constructing the tank.
17. Storage Tanks
Storage tanks can be divided into the following types:
1. Atmospheric storage
2. Pressure storage
3. Refrigerated storage
18. Storage Tanks
1. Atmospheric storage Tanks
- Applied to tanks operating at or near atmospheric pressure.
- They are used to hold liquids which will not vaporize at ambient
temperature.
19. Storage Tanks - Atmospheric Tanks
Atmospheric tanks are categorized primarily as follows:
1. Open top (no roof)
– has no roof and may store or process non-volatile liquids such as water, brine, etc.
2. Fixed roof
– Fixed roof tanks, such as cone roof or umbrella roof are used to store low vapor
pressure liquids which will not vaporize at temperature below 120oF.
– Generally used for gas oil, water, chemicals.
• Cone roof tank
• Dome roof tank
3. Floating roof
– Floating roof such as hard top pan and pontoon roof types eliminate the vapor
space above the liquid, allows storage of higher vapor pressure materials.
– Generally used for crude oil, gasoline, napthas
• External Floating roof
– Single Deck type
– Double Deck type
• Internal Floating roof
20. Open Top Tank
• This type of tank have no roof and are used to store,
– City Water
– Fire Water
– Cooling Water
21. Fixed Cone Roof Tank
• Fixed cone roof tanks are well
known type of storage tanks,
constructed over 100 years ago and
provided mostly with self
supporting roof structures.
• For large diameter tanks column
supported roofs are used.
Fixed Dome Roof Tank
• These tanks have roof shape similar to
dome.
• These tank roofs can be self supporting
structure hence no column supports are
necessary.
22. Floating Roof
• Emission of oil vapour represents:
– Considerable monetary loss termed
as “wastages”.
– Harmful long-term consequences to
environment.
• In-order to reduce these vapour
losses Floating roofs are used.
• In these types of roofs there is no
vapor space which greatly reduces
the emission arising due to
breathing loss and evaporative
loss.
23. Storage Tanks - Pressure Storage Tanks
2. Pressure storage tanks
– applies to vessels designed to withstand pressures sufficient to keep liquid
stored from vaporizing. Used for high vapor pressure liquid such as butane,
propane etc.
Spheres
– Generally used to store high vapor pressure liquid
– Advantage is that it can contain the greatest amount of liquid for a given
amount of steel.
– A sphere can also withstand greater pressures with a given plate thickness
than cylindrical vessels.
24. Storage Tanks - Refrigerated Storage Tanks
3. Refrigerated storage tanks
• Refers to low temperature/cryogenic storage
• This type is used for gases that liquefy under pressure at atmospheric
temperature.
• In cryogenic storage the gas is at, or near to, atmospheric pressure and
remains liquid because of low temperature.
• Cryogenic refers to temperature below -10oC
25. Tank structure
• Major tanks components are as follows,
• Tank Bottom
• Tank Shell
• Wind Girders
• Roof
• Stairway
26. Tank - Bottom
• Bottom / Floor design – Designed to, permit complete draw-off, minimize
product contact and to utilize maximum tank capacity and prevention of
corrosion of bottom plate.
• Two types of tank flooring are:
– Cone down bottom (Bottom down)
• Generally, bottom down is design for cone roof tanks. Centre of the flooring is
installed with drain pit. Water in the tank is accumulated in the pit (lowest point of
the bottom plate / floor).
– Cone up bottom (bottom up)
• Generally, this type of design is used for floating-roof tanks, 3 to 4 collector pits are
installed, close to the shell plate. Each of the pit is provided with a water draw-off
line. However, only one is connected to the closed water draw system in PPMSB.
27. Wind Girders
• Primary Wind Girder
• Open Top tanks & Floating Roof tanks are provided with primary wind girders in
order to maintain roundness of tank when tank is subjected to wind load.
• The wind girder shall be in the form of a ring located on the outside of the tank
shell, approximately 1 m below the top of the uppermost shell course. The top of
the uppermost shell course shall be provided with a top curb angle.
• Wind girders may be constructed from formed plate sections, by welding. The outer
periphery of the wind girder may be circular or polygonal.
• Secondary Wind Girder
• Tank may require secondary rings to maintain roundness over the full height of the
tank shell under wind and/or vacuum conditions.
• There are basically, additional stiffening rings. Continuous welding (full
penetration butt welds) shall be used for all connections of the secondary wind
girders.
28. Tank Accessories
• Mixers
• Heating coil
• Foam system
• Cooling water system
• Cathodic protection system
• Earthing and lightining arrestor
• Flame arrestor
• Level indicators
• Tank venting
29. Mixers
Mixing equipment can be installed in vertical tanks in order to:
• Blend or homogenize components and products, including bitumen.
• Control tank bottom products - usually for crude oils. In this case it is not
necessary to mix the whole tank contents but to create a flow pattern in the
lower part of the tank so that the solids are kept in suspension.
30. Tank Heating
• Products which require to be heated in order to facilitate movement or
loading into transport units need to be heated to the minimum
temperature that will ensure economic pumping and loading.
• This may be achieved by providing:
– heating coils inside the storage tanks,
– electrical heating elements,
– suction and/or line heaters, or
– a combination of these heating methods.
31. Thermal Insulation
Thermal insulation is applied to storage tanks for the following reasons:
• Heat conservation where heated products are being handled. In such cases
it is usual to insulate both the shell and roof plates.
• To minimize evaporation losses as a result of solar heat. In these
circumstances it is usual that only the roof is insulated. As an alternative to
roof insulation, floating covers may be considered for Class I products.
• For personnel protection - to prevent injury that may result by coming into
contact with hot surfaces.
32. Foam System
• The foam system are used for fire prevention, control or direct
extinguishment of any flammable or combustible liquid fire within the
tank.
• There are two types of systems employed in storage tank fire protection,
viz.
– A Fixed System is a complete installation piped from a central foam station, discharging
through fixed discharge devices on the hazard being protected. Foam proportioning
components are permanently installed.
– A Semi Fixed System is an installation where the hazard is equipped with fixed
discharge device(s) which connect to piping that terminates a safe distance from the
hazard. Foam producing materials are transported to the scene after the fire starts and are
connected to the piping.
• In accordance with NFPA Standard No. 11, there are three accepted
methods of protecting cone roof tanks:
– Surface (Foam Chamber) Method
– Subsurface Method
– Portable Foam Nozzle and Monitor Method
34. Cooling Water System
• Despite taking all reasonable precautions as demanded by governing
standards, a fire in an individual storage tank will generate significant
radiant heat, which can damage and / or ignite adjacent tanks which would
not otherwise be directly involved.
• A deep-seated fire in the smallest diameter tank can create major problems
unless cooling water is applied to its close neighbours.
35. Cathodic Protection System
Corrosion of Steel Storage Tanks
• Corrosion is the deterioration of metal due to reaction with the
environment. Corrosion occurs when;
– Areas with different electrical potentials exist on metal surface
– These areas are electrically connected
– Areas are in contact with electrolyte like moist soil in contact with tank bottom.
Water and sludge are the electrolytes for internal bottom surface.
Forms of Corrosion:
– General Corrosion leading to general metal loss and thinning
– Pitting due to localized actions ( metal loss may be concentrated within
relatively small area and other near area may be unaffected)
36. Cathodic Protection System
Cathodic Protection Methods
• Cathodic protection is the technique for preventing corrosion by making entire
surface of the metal to act as cathode of an electrolyte cell. There are two methods
commonly used;
– Sacrificial Anode
– Impressed current
Sacrificial Anode System (Galvanic System):
• This system involves an anode buried in soil, but electrically connected to the
structure (cathode). The anode is thus corroded (sacrificed) and metal surface is
protected. Metals commonly used as anodes are magnesium and zinc ( cast or
ribbon type). They are either buried beneath the bottom are distributed around the
perimeter of the tank.
Impressed Current System
• This system uses Direct Current (DC) usually provided by a rectifier. DC flows
from the rectifier to the buried impressed current anode.
• Power source include a step down transformer (reduces AC supply voltage) and
rectifying element to provide DC output.
• Impressed current anodes are of graphite, steel, high silicon cast iron or mixed
metal oxide on titanium.
38. Venting
The Need for Venting Equipment
• Protect Tank Integrity when Pumping In and Out
• Minimize Evaporation Losses (Cost Savings)
• Accommodate Thermal Effects
• Overpressure Due to Fire Near Tank (Emergency)
• Proper Vapor Transfer Control for Low-Pressure Systems
• Prevent Product Contamination
• Reduce Internal Tank Corrosion
• Comply with Clean Air Act Mandates
39. Flame Arrestor
• Flame arrestor is designed to stop the propagation of flame from ignited
flammable liquid vapours with low flash points.
• They prevent flame propagation by absorbing and dispatching heat thereby
reducing the temperature of the flame front preventing ignition behind the
cell element.
• Flame Arrestor can be installed either vertically or horizontally and is
available in aluminium, carbon steel or stainless steel.
• The cell element is available in stainless steel and special materials are
available on request.
41. Rim Seal Fire Protection System
• Rim Seal Fire Protection System is a
fully automatic detection cum
extinguishing system. The system is
designed and manufactured for
extremely fast detection and extinction
of rim seal fires as per the International
Safety Standards.
42. Rim Seal Fire Protection System
• To understand the complete working philosophy of the system, the system can be
divided in the following sub-systems:-
– Linear Heat Detection System.
– The Foam Based Extinguishing System.
– Fire Alarm Panel & Automation.
• The working of the detection unit is based on the principle of rate of rise in
temperature and maximum temperature beyond the pre-configured parameters,
which is sensed by means of a microprocessor based intelligent evaluation unit. The
Sensor element, i.e. the Stainless Steel / Copper Tube, which is in non-pressurized
state (ambient pressure only) senses the rate of rise in temperature (pressure) and
triggers an audio visual alarm simultaneously activating the extinguishing systems.
The Advance Detection System is Decentralize and has Pre Alarm facility for early
warning.
