Sources of Ignition and Hazardous Area Classification Core

Sources of Ignition and Hazardous Area Classification Core Likelihood of Ignition Factors of Explosion What factors influence the likelihood of explosion? We must work to prevent loss of containment and reduce the consequences when it happens. 1

Learning Objectives By the end of this lesson, you will be able to: Identify the ignition characteristics of fuel Explain the probability of leak ignition by release rate category Ignition Characteristics of Fuel Ignition Characteristics of Fuel Easily Ignited Fuel Ignition Energy (millijoules) Hydrogen Sulfide 0.07 Ethylene 0.12 Acetylene 0.017 Hydrogen 0.019 Less Easily Ignited Fuel Ignition Energy (millijoules) Minimum ignition energy normally occurs at ~ midpoint of flammable range Point of reference: A person typically discharges 10 30 mj exiting an automobile or walking across a carpet Methanol 0.14 Methane 0.29 Ethane 0.24 Propane 0.25 Normal Butane 0.25 2

Probability of Leak Ignition Release Rate Category Release Rate lbs/s (kg/s) Gas Leak (probability of ignition) Oil Leak (probability of ignition) Tiny <1.1 (<0.5) 0.005 0.03 Small 1.1 11 (0.5 5) 0.04 0.04 In terms of the release rate of hydrocarbons Medium 11 55 (5 25) 0.10 0.06 Large 55 441 (25 200) 0.30 0.08 Massive >441 (>200) 0.50 0.10 UKHSE Offshore Leaks Database (1991-2002) 2312 Leaks 6.2% of the leaks found a source of ignition Liquid leaks were more likely to ignite than gas leaks Always consider the operating environment from which data were drawn A large release might be too rich to ignite close to the point of release A small release may be more likely to be in its flammable range while it is near ignition sources 3

UKHSE Offshore Leaks Database (2001-2008) # of releases ~ 5 6 % ignited Do you think there has been a change since 2002? # ignited UKHSE Learning Objectives You will now be able to: Identify the ignition characteristics of fuel Explain the probability of leak ignition by release rate category 4

Sources of Ignition and Hazardous Area Classification Core Sources of Ignition Learning Objectives By the end of this lesson, you will be able to: Identify common non-electric sources of ignition and their design alternatives Indicate the primary controls for non-electric sources of ignition Identify commonly overlooked ignition sources Describe how electrical equipment can become a source of ignition 5

The Fire Triangle Safety Incidents Description Frequency No. % No Ignition Involved 234 41.6 Auto Ignition 82 14.6 Unknown 73 13.0 Flame from Furnace, Cutting Torch, Engine and Other 61 10.9 Hot Surface 26 4.6 Lightning 19 3.4 Autoignition is a major source of ignition in the refining and petrochemicals sector and was involved in 14.6% of the incidents Spark from Friction, Grinding or Impact 19 3.4 Static Electricity* 18 3.2 Electrical Equipment 13 2.3 Welding Arc 9 1.6 Pyrophoric 7 1.2 Match 1 0.2 Total: 562 100.0 * May be on the high side. Often used when no other source of ignition is identified. 6

Canadian Upstream Oil & Gas Industry Electric Arc and Sparks 8% Friction / Mechanical Sparks 8% Vehicle Ignition 8% OpenFlame Welding Arc 22% Adiabatic Compression 10% Pyrophoric Iron Sulphide 10% Hot Surfaces 12% Static Electricity 22% 7

Non Electric Ignition Sources Offshore UK Most Common Hot turbine or engine exhaust Hot work welding Glycol regenerator firetube/burner Flare Lightning Offshore Gulf of Mexico Most Common Hot turbine or engine exhaust Hot work welding/cutting torch Glycol regenerator firetube/burner Electrical shorts The three major ignition sources include hot turbines, hot work, and Glycol regenerators fire tubers/burners. 8

Hot Surfaces The most common hot surfaces are gas turbine or diesel engine exhausts, and there are diesel and lube oil fires every year. Fires are also ignited by exposed firetubes and hot exhaust. As a rule, a hot surface must be significantly greater than the autoignition temperature if the fuel is unconfined. Unless there is something to hold the hydrocarbon against that surface, it may not be in contact with the hot surface long enough to reach its auto-ignition temperature. If that fuel is held against the hot surface, such as a flammable liquid that has soaked into a fibrous insulation, then spontaneous ignition can occur well below the auto ignition temperature. Key Learning Points Most Common: Gas turbine/engine exhaust diesel and lube oil fires most common Exposed firetubes/exhaust Experience has shown that hot surface temp normally must be significantly greater than Autoignition temperature. Exception: Slow oxidation of trapped fuel local high temperatures Fuel smolders ignite Hot surfaces in an enclosed and therefore poorly ventilated space, such as a boiler house, pump house, or compressor house, will not need to be as far above the autoignition temperature as would be the case if the fuel was not confined. 9

Autoignition Autoignition and slow oxidation are both forms of spontaneous ignition. Autoignition takes place when an ignitable mixture is hot enough to ignite without anything else, such as a spark or a flame, to cause ignition. Slow oxidation can take place at normal temperatures if heat can t escape. Oil soaked rags, for example, will slowly oxidize in air. If they are exposed such that heat can escape this is not likely to be a problem. If the rags are piled together the heat release may be trapped. As the temperature rises, so does the reaction rate, and the rags are likely to smolder, then burn. The process by which a lube oil leak into insulation can lead to slow oxidation and then to fire, discussed a little earlier, is another example of slow oxidation. 10

Other Physical Ignition Sources Mechanical Ignition Friction Vibration Sparks Impact Controls Separation of fuel and ignition sources (PTW system) Protection from friction, impact and vibration Commonly Overlooked Ignition Sources Moderate temperature sources that may cause spontaneous ignition, eg. hot oil soaked insulation Electrical (non-power), eg. static, stray currents, lightning Physical, eg. compression energy, friction, impact Chemical, eg. pyrophoric materials 11

Primary Controls Always consider the inherently safer design alternatives first Other Types primary of controls protection include: Inherent Always separate fuel and Passive ignition sources if not by design then by work permits Active Open flames always Procedural require hot work permits Non open flame ignition sources always require at minimum general/cold work permits plus consideration for hot work permits 12

Electrical Equipment as Ignition Source Hazardous Area Classification Determines which areas are nonhazardous, and classifies the potentially hazardous area in two or three categories Infrequent and of short duration or a normal and expected state? HAC also groups ignitable atmospheres so that atmospheres with similar degrees of danger are grouped together If HAC is done properly, we know what types of equipment to use in what areas Electrical Equipment as Ignition Source Hazardous Area Classification Determines which areas are nonhazardous, and classifies the potentially hazardous area in two or three categories Use of Approved Electrical Equipment Dependent on Hazard Analysis Classification Use of qualified personnel Equipment should be correctly installed, commissioned, and maintained 13

Learning Objectives Now you will be able to: Identify common non-electric sources of ignition and their design alternatives Indicate the primary controls for non-electric sources of ignition Identify commonly overlooked ignition sources Describe how electrical equipment can become a source of ignition 14

Sources of Ignition and Hazardous Area Classification Core Hazardous Area Classification and Design Alternatives Learning Objectives By the end of this lesson, you will be able to: Identify the purpose of Hazardous Area Classification Describe Hazardous Area Classification and design alternatives Compare the three IEC zones and the two NEC divisions Describe the correlation between area classification and risk assessment 15

Typical Hazardous Area Classification (OSHA) Group Designations Group A (most hazardous) Acetelyne Group D (least hazardous) Hydrocarbons, fuels, solvents Groupings are based on fire/explosion hazard risk related to the following properties: Flammable range Ignition energy Flame temperature Maximum experimental safe gap (MESG) 16

Gas Group Comparisons IEC Group 1 Gas Methane North America Group A Acetylene Gas Group 2A Group 2B Group 2C Propane Butane Heptane Benzene Ethylene Diethyl Ether Benzene Butane Ethane Heptane Methane Group B Group C Group D Hydrogen Ethylene Cyclopropane Benzene Butane Ethane Heptane Methane NEC National Electrical Code IEC International Electrotechnical Commission Area Classification Risk Assessment IEC s zone 2 is the same as the NEC s Division 2 In Division 1, we expect that a hazardous atmosphere may exist under normal conditions In Division/Zone 2, we expect that a hazardous atmosphere may exist under abnormal conditions for a short time 17

Protection Methods 1 Locate the electrical equipment/device of concern in a nonhazardous area 2 3 Utilize explosion-proof enclosures Utilize intrinsically safe electrical components 4 Purging & pressurization Enclosures are designed to contain an internal explosion and prevent the escaping gases from igniting the surrounding atmosphere Intrinsically Safe Design A circuit in which any spark or thermal effect is incapable of causing ignition of a combustible mixture Mainly accomplished by limiting the available power (voltage & current) in a circuit Mostly used for instrumentation, signals & controls 18

Protection Protection by Containment All 3 elements of the fire triangle can be present inside the enclosure Protection by eliminating the ignition source Purging and Pressurization Purging and Pressurization prevents ingress of the external atmosphere into the enclosure by maintaining protective gas at a positive pressure normally use instrument air Purging is mainly a start-up operation to remove flammable gas/vapor from a protected enclosure typically 5-10 volume changes Pressurization prevents the entry of flammable gas/vapor into the protected enclosure typically 0.1 (2.5 mm) water Any electrical equipment cabinets, electric motors, etc. 19

Purged and Pressurized Electrical Equipment Enclosures Type Description X Reduces enclosures classification from Division 1 to non-hazardous Y Reduces enclosures classification from Division 1 to Division 2 Z Reduces enclosures classification from Division 2 to non-hazardous Center for Chemical Process Safety (CCPS), Guidelines for Engineering Design for Process Safety, Second Edition. Wiley, 2012, Table 7.1 page 319 Intrinsically Safe and Non-Incendive Equipment Type Description Where Used Intrinsically Safe Non-incendive Will not ignite the most ignitable concentration of the hazardous material at 1.5 times the highest energy possible under normal conditions, under 1.5 times the energy of the worst single fault, and under the energy of the worst combination of two faults. Will not ignite the most ignitable concentration of the hazardous material under normal conditions. Class I, Division 1 Class I, Zone 0 Class II, Division 1 Class III Locations Class I, Division 2 Class II, Division 2 Class III Locations Center for Chemical Process Safety (CCPS), Guidelines for Engineering Design for Process Safety, Second Edition. Wiley, 2012, Table 7.2 page 321. 20

Learning Objectives You are now able to: Identify the purpose of Hazardous Area Classification Describe Hazardous Area Classification and design alternatives Compare the three IEC zones and the two NEC divisions Describe the correlation between area classification and risk assessment 21

Sources of Ignition and Hazardous Area Classification Core Non-Power Electrical Sources of Ignition, and the Reequipments for Ignition by Static Electricity Learning Objectives By the end of this lesson, you will be able to: Identify and describe non-power electrical ignition sources Identify non-power ignition controls 22

Non-Power Electrical Ignition Sources Static Electricity Four conditions must combine to create an electrostatic ignition: 1 Streaming current is the most common charge generation mechanism followed by mixing, filtering and any mechanism that creates turbulence such as spray nozzles for tank cleaning 4 2 3 A means of an isolated conductor is the most common means of accumulating a charge When the isolated conductor comes into near contact with a grounded object the spark will jump A spark in the presence of HC vapors = ignition (refer back to slide #5 for ultra low ignition energy requirements) Non-Power Electrical Ignition Sources Static Hazards Personnel grounding Liquids handling (a significant issue when loading marine vessels, tank trucks and rail cars) Many highly refined products are static accumulators because of their low conductivity Solids handling (e.g., ignition of flammable liquids during hand addition of powders occurs frequently; personnel electrical shock hazard) Static Controls Follow API 2003 guidance for marine, truck and rail loading Identify opportunities for static ignition and remove one or more of the four necessary conditions Employ good bonding and grounding practices API 2003 states: Static discharges from clothing are very unlikely to ignite ordinary hydrocarbon gases in air static charging of personnel has not proven to be a significant safety problem in normal petroleum industry operations. 23

Non-Power Electrical Ignition Sources Four Requirements: Generation Accumulation A spark gap Ignitable atmosphere API 2003 states: Static discharges from clothing are very unlikely to ignite ordinary hydrocarbon gases in air static charging of personnel has not proven to be a significant safety problem in normal petroleum industry operations. Non-Power Electrical Ignition Sources Lightning Lightning strike of flammable and combustible liquids storage tanks is a common occurrence External Floating Roof tanks with poor primary and secondary seal management are likely candidates for fires following lightning strikes Fixed roof tanks that vent to atmosphere are also likely candidates for fires ignited by lightning Lightning Controls Frequent inspection and maintenance of lightning protection systems 24

Non-Power Electrical Ignition Sources Stray Currents Radio frequencies Overhead high voltage transmission lines Cathodic protection Electrical heat tracing Unsynchronized electrical systems between marine vessel and shore facility Stray Current Controls Isolating flanges Sacrificial anodes Stray currents are a less likely ignition source when fuel is removed from the fire triangle Learning Objectives Now you will be able to: Identify and describe non-power electrical ignition sources Identify non-power ignition controls 25

Sources of Ignition and Hazardous Area Classification Core PetroAcademyTM Process Safety Engineering Skill Modules Process Safety Risk Analysis and Inherently Safer Design Core Process Hazards Analysis and Layers of Protection Analysis Core Leakage and Dispersion of Hydrocarbons Core Combustion Behavior of Hydrocarbons Core Sources of Ignition and Hazardous Area Classification Core Specific Plant Systems and Equipment Core Relief and Flare Systems Core Historical Incident Databases, Plant Layout and Equipment Spacing Core SIS, Monitoring and Control Core Fire Protection Systems Core 26