Ignition Sources (A complete and informative document) by SAAD ABDUL WAHAB

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IGNITION source

A device or item that is capable of generating sparks or enough heat to produce combustion..

or

Any process or event capable of causing a fire or explosion. Open flames, sparks, static electricity, and hot surfaces are all possible ignition sources.

or

A heat source having sufficient energy to initiate combustion of a material.

or

Anything that produces or can produce a spark or flame, intentionally or otherwise, is a potential ignition source
or
Chemically, an ignition source is anything that is required to have the threshold potential to initiate the combustion reaction, this threahold potential may be (stored) in any any form of energy like mechanical, electrical, heat, light, chemical, potential, etc. 

Likewise we need to have a pistol or fuse for detonation of explosive charge, a high energy fast moving neutron to be bombarded to the heavy nucleus of a radioactive element for initiation of nuclear fission chain reaction, also like we use an initiator to start a polymerization reaction. 

Incase of fires, air (21% OXYGEN) or directly oxygen or any source of oxygen like oxidants and oxidizing agents, means presence of oxygen is an optimum and essential requisit of reaction medium, FUEL is an object containing rest form of stored potential and IGNITION SOURCE is the stimulant or initiator used to supply threshold energy to the FUEL to initiate the combustion reaction in an oxygenated reaction medium. The products of this exothermic combustion reaction are (physically) Flame (mixture of Heat & Light energy) and smoke, chemically gases comprising COx, SOx, NOx and H2O (depending upon the chemical nature of FUEL), radiations etc.

Any fire can be converted into explosion depends whether the combustion reaction was carried out in an open atmosphere or in a closed/insulated system, as the combustion reaction starts simultaneously with the emiision of radiations, heat energy and gases generating pressure, if the FUEL is enclosed in a container or shell, then the IGNITION SOURCE will become a PISTOL or FUSE spontaneously, that we use in HE Missiles, as the generated internal pressure approaches to the corresponding magnitude of shell/container's pressue limits, a very small internal activity would be required to collapse the stablished limiting equilibrium between internal pressure and containers material of construction. the positive collapse of this limiting equilibrium will termed as explosion, now the products of this explosion would be High energy sound waves, splinters, Heat, Light, explosive particles, their combined effect can be as much destructive as the stablity of material of construction of container was, also as the nature and amount of FUEL was charged/filled in that container.

Explosions and their destructibility is measured in the detonation velocity of explosive charge, brisance or shatering capability, as the shell/container explodes, an electromagnetic shock wavefront formed and travels with some particular detonation velocity in all possibly available directions, whose ultimate effect varies with the nature of explosives.

For more details on explosives, read my article : 
http://saadappliedianengineer.blogspot.com/2013/01/presentation-on-explosives-potential.html

Before going to IGNITION SOURCES, its relatable to know the classes of fire classified by different countries..

Comparison of fire classes

American	European	Australian/Asian	Fuel/Heat source
Class A	Class A	Class A	Ordinary combustibles
Class B	Class B	Class B	Flammable liquids
	Class C	Class C	Flammable gases
Class C	UNCLASSIFIED	Class E	Electrical equipment
Class D	Class D	Class D	Combustible metals
Class K	Class F	Class F	Cooking oil or fat

Australia

Type	Pre-1997		Current	Suitable for use on Fire Classes (brackets denote sometimes applicable)
Water	Solid red		Solid red	A
Foam	Solid blue		Red with a blue band	A	B
Dry chemical (powder)	Red with a white band		Red with a white band	A	B	C		E
Carbon dioxide	Red with a black band		Red with a black band	(A)	B			E
Vaporising liquid (non-halon clean agents)	Not yet in use		Red with a yellow band	A	B	C		E
Halon	Solid yellow		No longer produced	A	B			E
Wet chemical	Solid oatmeal		Red with an oatmeal band	A					F

In Australia, yellow (Halon) fire extinguishers are illegal to own or use on a fire, unless an essential use exemption has been granted.

United Kingdom

The UK recognizes five fire classes:

• Class A fires involve organic solids such as paper and wood.
• Class B fires involve flammable or combustible liquids, including petrol, grease, and oil.
• Class C fires involve flammable gases.
• Class D fires involve combustible metals.
• Class F fires involve cooking fat and oil.

Type	Old code		BS EN 3 color code	Suitable for use on fire classes (brackets denote sometimes applicable)
Water	Signal red		Signal red	A
Foam	Cream		Red with a cream panel above the operating instructions	A	B
Dry powder	French blue		Red with a blue panel above the operating instructions	(A)	B	C		(E)
Carbon dioxide CO2	Black		Red with a black panel above the operating instructions		B			E
Wet chemical	Not yet in use		Red with a canary yellow panel above the operating instructions	A	(B)				F
Class D powder	French blue		Red with a blue panel above the operating instructions				D
Halon 1211/BCF	Emerald Green		No longer in general use	A	B			E

United States

Fire Class	Geometric Symbol		Pictogram	Intended Use	Mnemonic
A	Green Triangle			Ordinary solid combustibles	A for "Ash"
B	Red Square			Flammable liquids and gases	B for "Barrel"
C	Blue Circle			Energized electrical equipment	C for "Current"
D	Yellow Decagon (Star)			Combustible metals	D for "Dynamite"
K	Black Hexagon			Oils and fats	K for "Kitchen"

 

Most Common Ignition Sources:

1. Heat, 
2. Electrostatic charges, 
3. Oxidizing agents, 
4. Electric spark, 
5. Explosive dust, 
6. Inflammable vapor concentration, 
7. Mechanically & electrically generated sparks, 
8. Hot surfaces, 
9. Radio frequency (RF) electromagnetic waves from 104 Hz to 3x1012 Hz, 
10. Stray electric current, 
11. Cathodic corrosion protection, 
12. Flames & hot gases, 
13. Electromagnetic waves from 3x1011Hz to 3x1015Hz, 
14. Ionizing radiations, 
15. Ultrasonics, 
16. Adiabatic compression, 
17. Shock waves, 
18. Chemical reactions including self ignition of dust, 
19. Pyrophoric materials like Pyrophoric Iron Sulphides, 
20. Pyrophoric reaction that occurs when sodium is exposed to water, 
21. Scorching sunlight (UV radiations), 
22. Light converging/focal point, 
23. Exhausts of combustion engines, 
24. Thermite action, 
25. Batteries, 
26. Electrical arcs (High energy fast moving electrons), 
27. Sudden decompression, 
28. Catalysts, 
29. LASERs, 
30. Fiber optic light sources, 

Identify Sources of Ignition

You can identify the potential ignition sources in your premises by looking for possible sources of heat which could get hot enough to ignite material found in your premises. These sources could include:

• smokers' material, e.g. cigarettes, matches and lighters;
• naked flames, e.g. gas or liquid-fuelled open-flame equipment;
• sparks from burning products, e.g. bonfires in yards;
• vehicle exhausts;
• electrical, gas or oil-fired heaters (fixed or portable), room heaters;
• hot processes/hot work, e.g. welding by contractors or shrink wrapping;
• cooking equipment, hot ducting, flues and filters;
• extract fans for dust and fume removal systems, e.g. by build-up of debris;
• failure of temperature control thermostats on hot work/cooking processes;
• heat sources, such as gas, electric, microwaves, radio frequency, thermal fluids;
• steam pipes;
• frictional generated heat from mechanical equipment;
• static charge from mechanical equipment, e.g. conveyor belts;
• poor electrical installations, e.g. overloads, heating from bunched cables, damaged cable;
• faulty or misused electrical equipment, e.g. refrigeration defrost systems, fork lift truck charging units;
• light fittings and lighting equipment, e.g. halogen lamps or display lighting or overhead lights too close to stored products;
• hot surfaces and obstruction of equipment ventilation;
• spontaneous ignition and self heating, e.g. oil soaked rags, paint scrapings, crumb and batter residue; and
• arson.

Indications of 'near-misses', such as scorch marks on furniture or fittings, discoloured or charred electrical plugs and sockets, cigarette burns, etc., can help you identify hazards which you may not otherwise notice.

Example of potential ignition sources

Smoking Materials; e.g. cigarettes, lighters and matches.	Naked Flames.	Electrical, gas or oil-fired heaters (fixed or portable).
Hot processes, such as welding, cutting or grinding.	Engines, generators and boilers (fixed or portable).	Cooking facilities (permanent or temporary).
Machinery.	Faulty, misused and damaged electrical equipment and/or associated wiring installations.	Lighting equipment (fixed or portable).
Hot surfaces and the obstruction of equipment ventilation; e.g. photocopying and printing facilities	Friction from machinery bearings and drive belts.	Chemical reaction and /or storage incompatibility.
Static Electricity.	Metallic impact.	Arson.

Ignition sources of explosion

Besides explosive atmosphere made of air (oxygen) and flammable matter in the for of dust, gas or mist, also ignition source is necessary for the explosion. It is the third apex of the explosion triangle (combustible matter, oxygen, ignition source). Ignition source is, generally said, such effect, which produces energy to its surroundings and this energy is sufficient to ignite the explosive atmosphere in which this source occurs. Energy necessary for the ignition is depending on the type of the explosive atmosphere and characteristics of the dust or gas. Generally can be said, that for ignition of gaseous atmosphere only 10-1000 times lower energy is sufficient, comparing to dust atmosphere.

Despite of the fact, that there can be unlimited reasons for forming the ignition source (and telling them after the massive explosion is the most complicated part of the investigation), there is only limited number of ignition sources and many of them is even not sufficient for the ignition of majority of the matters. The complete list of the ignition sources with the information if the source is or is not relevant in normal conditions for gases or dust is in the following table.

List of ignition souces

ignition source	common reason	relevant for dusts	relevant for gases and vapours
hot surface	friction of the rotating parts, failures of the devices working with high temperature, damages of heat insulations, processing of the materials, failures of brakes, barings, rotating mechanisms	YES	YES
flames, glowing particles, sparks	furnaces, burning chambers, devices for drying, devices working with open fire,...	YES	YES
mechanical sparks	friction, impacts, abrassive processes (grinding, polishing), foreign objects in the technology, cutting, breakes, bearing, rotating mechanisms,...	YES	YES
electric devices (discharge sparks, hot surfaces)	switching on and off the electric circuits, releasing of the contacts and connections, electric arc and short connections, heating, damaged lightings, bulbs,...	YES	YES
stray electric current	reverse current, damaged insulations of high voltage cables and devices, failures in electric installations, magnetic induction, back current circuit failures,...	rarely (depending on the type of the dust and energy of the ignition source)	probably yes
static energy	failures of grounding, fast separation processes, friction	rarely (only the most sensitive dusts)	almost always
lightning	lightning itself, heating of the lightning conductor, static energy induction in the close surrounding of the lightning	YES	YES
high-frequency electromagnetic waves	TV and radio broadcasting transmitter failurs, measuring, army and medical devices failure, high frequency generators (drying, hardening, welding, cutting),...	rarely	sometimes (depending on the energy of the source)
electromagnetic waves	concentrated rays and waves (lenses, reflectors), lasers (including measuring devices), strong sources of radiation,...	yes, but depending on the energy	YES
ionizing radiation	X-rays, radioactive materials, chemical reaction caused by radiation (disruptive exotermic reactions), microwaves,...	yes, but depending on the energy	yes, but depending on the energy
ultrasound	absorption of ultrasound waves	depending on energy, but in normal conditions unrealistic	rarely
adiabatic compression and shock waves	heat produced during fast and strong adiabatic compressions, heat caused by pressure shock wave going through the pipeline	no, unrealistic in normal conditions	rarely
exotermic reactions (including autogenous ignition)	chemical reactions, flammable matters, biochemical processes, polymeration reactions,...	YES	YES

Important notice!

This table should never be understood as definitive and for all kinds of explosive atmospheres and conditions, because minimum ignition energy may vary in great range. Also these ignition sources can reach various energies depending on their origin (for example electromagnetic waves). If there is "rarely" or "depending on the conditions" in the table, it means during normal circumstances and in commonly used devices. Always keep in mind that theoretically any of these ignition sources may ignite any type of explosive atmosphere, during certain circumstances, so no ignition source can be fully ignored if there is at least theoretical chance of its appearance.

COAL Gases

FLAMMABLE/COMBUSTIBLE LIQUIDS 

(some OSHA defined Jargons)

OSHA Jargon	Definition
Boiling Point	The temperature at which a liquid changes to a vapor.
Bond Wire	A wire that connects two objects to reduce the build up of electrical charges between them. Bond wires are used to connect containers when transferring flammable and combustible liquids from one container to another to reduce the formation of harmful static electricity.
Bonding	Physically connecting two electrically conductive objects together to eliminate a difference in the static charge potential between them. Bonding often occurs between metal containers and is done using a bond wire.
Class IA Liquid	A flammable liquid with a flash point less than 73°F (22.8°C) and a boiling point less than 100°F (37.8°C). Examples of Class IA liquids include acetaldehyde and ethylamine, which are used in chemical processes.
Class IB Liquid	A flammable liquid with a flash point of less than 73°F (22.8°C) and a boiling point over 100°F (37.8°C). Examples of Class IA liquids include benzene and gasoline.
Class IC Liquid	A flammable liquid with a flash point between 73°F (22.8°C) below 100°F (37.8°C). An example of a Class IC liquid is hydrazine propyl alcohol.
Class II Liquid	A combustible liquid with a flash point between 100°F (37.8°C) and below 140°F (60°C).Examples of Class II liquids include acetic acid and kerosene.
Class IIIA Liquid	A combustible liquid with a flash point between 140°F (60°C) and 200°F (93.4°C). Examples of Class IIIA liquids include butyric acid and phenol.
Class IIIB Liquid	A combustible liquid with a flash point at or above 200°F (93.4°C). OSHA flammable and combustible liquid regulations do not apply to Class IIIB.
Closed Piping System	A piping system used to transport a liquid that is sealed to prevent vapors. Closed piping systems help prevents fires due to flammable or combustible liquids.
Combustible Liquid	A liquid that will ignite if it reaches its flash point and is provided with an ignition source. Combustible liquids have a flash point above 100° Fahrenheit (37.8°C).
Drum	A large metal storage container used for storing substances such as flammable and combustible liquids. OSHA-approved drums for flammable liquid storage must be equipped with safety features such as safety vents.
Drum Bung Opening	The opening of a storage drum located on the top of the container. Flammable and combustible liquids are transferred from drums to smaller containers via the drum bung opening.
Fire Flashback	The explosion of a container caused by a fire that occurs outside the container and then enters the container through the flammable or combustible liquid's vapors.
Flame Arrester Screen	A mechanical device installed on a storage tank or portable container nozzle designed to prevent the build up of flammable vapors and quickly extinguish a fire in the container by rapidly dissipating heat from the fire. It is made of double mesh wire and extends inside the container from the nozzle.
Flammable Liquid	A liquid that will ignite if it reaches its flash point and is provided with an ignition source. Flammable liquids have a flash point below 100° Fahrenheit (37.8°C) and can typically ignite at room temperature.
Flash Point	The lowest temperature at which a liquid produces enough vapor to form an ignitable mixture. Liquids with low flash points pose the greatest danger.
Ground Wire	A wire that connects an object to a copper rod drilled into the earth that helps prevent the build up of electric charges. Ground wires are attached to the metal drums used to store flammable liquids to prevent static electricity.
Grounding	Physically connecting a conductive object with a rod driven into the earth using a wire. Grounding provides a conductive path for electrical charges and carries them away from objects to prevent the build up of static electricity.
Hazard Communication	The means through which employers inform their employees about hazards in the workplace, including training and MSDS.
Ignition Source	Any process or event capable of causing a fire or explosion. Open flames, sparks, static electricity, and hot surfaces are all possible ignition sources.
Incipient Stage Fire	A fire in its beginning stage. Incipient stage fires can be controlled with portable fire extinguishers and small hose systems.
Material Safety Data Sheet	Mandatory information that must accompany almost every chemical in the workplace, including flammable and combustible liquids. An MSDS includes details such as the risks, precautions, and first aid procedures associated with the chemical.
Occupational Safety And Health Administration	A government agency that sets the standards for working conditions in the United States and ensures that employees work in safe and healthy environments. The Occupational Safety & Health Administration is abbreviated as OSHA.
Oily Waste Can	A container used for disposing rags soaked in flammable and combustible liquids. The oily waste can features a self-closing lid.
Safety Can	A portable container used for storing one to five gallons of flammable or combustible liquids. The OSHA-approved safety can must include safety features such as a safety vent.
Safety Disposal Can	A container used for storing and disposing up to five gallons of industrial waste, including flammable and combustible liquids.
Safety Pump	An OSHA-approved device used for transferring liquids from storage drums to portable containers that is faster and safer than the self-closing faucet.  The safety pump attaches directly to the drum's opening.
Safety Vent	A vent or opening that prevents the contents in a container from reaching temperatures that would cause them to explode. Most types of OSHA-approved containers for flammable and combustible liquids contain a safety vent.
Self-Closing Safety Faucet	An OSHA-approved device used for transferring liquids from storage drums to portable containers. The faucet must be used with a bond wire between the storage drum and the nozzle of the portable container.
Spring-Closing Lid	A lid using spring action to close automatically after use to limit the amount of oxygen and fuel risk when storing flammable and combustible liquids.  The spring-closing lid is an important safety feature found on OSHA-approved safety cans and some other storage containers for flammable and combustible liquids.
Static Electricity	An electrical charge that builds up due to rubbing contact between two dissimilar materials. Static electricity is an ignition source for flammable liquids.
Storage Cabinet	An enclosed container with shelving used to store various industrial materials. An OSHA-approved storage cabinet for flammable and combustible liquids must be made of metal or wood, must include certain safety features, and must be raised two inches (5.08 cm.) from the ground and be properly labeled.
Storage Room	A room used for storing various materials used in production. OSHA requires storage rooms to have an approved ventilation system for storing large amounts of flammable and combustible liquids.
Three-Point Lock	A locking mechanism installed on storage cabinet doors that secures doors at the top, bottom, and sides. The three-point lock is required by OSHA to secure cabinets containing flammable and combustible liquids.
Vapor	The gaseous form of a substance that is a liquid or solid at normal temperatures. The vapors of flammable and combustible liquids can ignite if fire or sparks are present.
Waste Drum	A container used for storing and disposing of large amounts of flammable and combustible liquid waste.

 

TABLE

Type of extinguishers

Test interval (years)

Soda acid (soldered brass shells) (until 1/1/82) Soda acid (stainless steel shell) Cartridge operated water and/or antifreeze Stored pressure water and/or antifreeze Wetting agent Foam (soldered brass shells) (until 1/1/82) Foam (stainless steel shell) Aqueous Film Forming foam (AFFF) Loaded stream Dry chemical with stainless steel Carbon Dioxide Dry chemical, stored pressure, with mild steel, brazed brass or aluminum shells Dry chemical, cartridge or cylinder operated, with mild steel shells Halon 1211 Halon 1301 Dry powder, cartridge or cylinder operated with mild steel shells

(1) 5 5 5 5 (1) 5 5 5 5 5 12 12 12 12 12

Extinguishers having shells constructed of copper or brass joined by soft solder or rivets shall not be hydro-statically tested and shall be removed from service by January 1, 1982. (Not permitted)