Intrinsic safety and flameproof apparatus in mines

1

MINE ENVIRONMENT ENGINEERING

ASSIGNMENT-1 MN331

Presented byPATI JAYA CHANDRA

113MN0480GROUP-1

2

INTRINSIC SAFETY AND FLAMEPROOF

APPARATUS IN MINES

3OVERVIEW

• What is Intrinsic Safety• Intrinsic safe design considerations• Advantages and Disadvantages• Flameproof apparatus• Flameproof Enclosures• Statutory Guidelines• Choice of System between intrinsic safety and flameproof• References

4What is Intrinsic Safety?

• Intrinsic Safety is a technique used to prevent explosions, which could be caused due to sparking of electrical apparatus in hazardous areas.

• Intrinsic Safety is a concept that came out of the mining industry in the early 19th century

5What is Intrinsic Safety?

• At that time, a lot of mining accidents used to happen, many of which were traced to sparks that were generated by electrical circuits, which were used in mine lighting, signaling equipment and the like.

• To reduce the number of these accidents, it was proposed to use electrical equipment that could not generate sparks that could ignite the Firedamp. Thus was born Intrinsic Safety.

6Intrinsic Safe Design Considerations

• Several different agencies develop standards for intrinsic safety, and evaluate products for compliance with standards.

• Agencies may be run by governments or may be composed of members from insurance companies, manufacturers, and industries with an interest in safety standards.


• In the EU the standard for intrinsic safety certification is the ATEX Directive, while in other countries around the world the IECEx standards are followed.

• Standards agencies around the world harmonize activity so that intrinsically safe equipment manufactured in one country eventually might be approved for use in another without expensive testing and documentation.


There are three components, and all three together make a field device intrinsic safety.

• The primary device, like the transmitter, needs to be intrinsic safe

• The power for the device should come though the intrinsic safety barrier

• The field wiring should not be capable of causing a fire


Designing an electronic circuit for a device placed in a hazardous area should consider:

• Voltage and current are kept low so no spark can occur, and should they occur, possess so little energy that they are unable to ignite an explosive atmosphere.


• Resistors to be used reduce/constrain the instantaneous release of the charge from capacitors/diodes.

• As a high surface temperature could cause ignition, the maximum temperature of any faulty component on a circuit board must be within permissible limits As a high surface temperature could cause ignition, the maximum temperature of any faulty component on a circuit board must be within permissible limits.

11Advantages of Intrinsic Safety

• The most important advantage is that it is the only technique that is allowed to be used under Zone 0 of the IEC Classification system for hazardous areas. Other techniques like explosion proof or any of the many other methods of protection cannot be used in Zone0.

• Eliminates the possibility of explosion


• Least expensive and easiest to install of all the protection methods

• Ideal for low power devices

• Little to no maintenance required.

• Accepted throughout the world


• The same IS equipment usually satisfies the requirements for both dust and gas hazards.

• The installation and maintenance requirements for intrinsically safe apparatus are well documented, and consistent regardless of level of protection.

14Disadvantages of Intrinsic Safety

• Documentation required for IS circuits and installation

• Only suitable for low-power devices

• Improper installation and maintenance of intrinsically safe field wiring can compromise the safety of equipment complying with the design standards for intrinsic safety.

15FLAME PROOF APPARATUS

In coal mines, where the natural gas methane (fire damp) may occur, and in oil refineries, chemical plants, gas works, hospitals or any other place where a flammable gas or vapor may be present, it is a statutory requirement that safeguards be applied to electrical equipment to prevent ignition of the gas or vapor and consequent explosion or fire.

16FLAME PROOF APPARATUS

• Two systems of protection against such dangers have been evolved:

• Flameproof (FLP) and Intrinsically Safe.

• Flameproof, the only method generally applicable to lighting and power installations, depends upon mechanical design to prevent any explosion inside the case of the apparatus or machine from igniting the external atmosphere.

17British Standard 229 gives this definition

A flameproof enclosure for electrical apparatus is one that will withstand, without injury, any explosion of the prescribed flammable gas that may occur within it under practical conditions of operation within the rating of the apparatus and will prevent the transmission of flame such as will ignite the prescribed flammable gas which may be present in the surrounding atmosphere

18British Standard 229 gives this definition

• The first requirement is met by the provision of a substantial case, the second by ensuring that joints and other openings (such as bearings) provide a sufficiently long and restricted flame path to prevent external ignition

• Certificates of Flameproofness in any gases or vapours are issued by the Ministry of Power.

19 DGMS

According to DGMS, India as mentioned in CMR

• “Flame proof apparatus” means an apparatus that can withstand without injury any explosion of the inflammable gas that may occur within it and can prevent the transmission of flame such as will ignite the inflammable gas which may be present in the surrounding atmosphere

20Statutory Guidelines according to IS: 9559 – 1980

• The transformers shall be in flameproof construction where statutorily required and shall be of an approved type.

• Rope Haulage Equipment - The smaller haulages may be driven by flameproof Squirrel cage induction motor with flameproof direct-on- line starter or star-delta starters.

21Statutory Guidelines according to IS: 9559 – 1980

• Hand-held coal drills shall, be of flameproof construction and rated between 0.93 and 1.1 kW at 125 V.

• Coal Cutting machines - The machines consist of a flameproof motor and controller and is connected to its control gear by a screened flexible cable with plug and socket assembly.

22IS 3682 (1966): Indian Standard Specification for Flameproof Alternating Current Motors for Use in Mines

• The requirements for flameproof enclosures of electrical machinery and apparatus for use in mines and such other places where flammable gases or vapors may exist or may originate inside the enclosure are covered by IS: 2148.1962

• This standard covers flameproof ac motors designed for use in mines and having insulated windings with class A, E and B insulation

23FLAMEPROOF ENCLOSURES

Types of Flameproof Enclosures

• A totally-enclosed motor ( TE ) is a motor so constructed that the enclosed air has no connection with the external air, but not necessarily air-tight.

• A totally-enclosed fan-cooled motor ( TEFC ) is a totally-enclosed motor with augmented cooling by means of a fan driven by the motor itself, blowing external air over the cooling surfaces and/or through the cooling passages, if any, incorporated in the motor.


• A totally-enclosed separately air-cooled motor ( TESAC ) is a totally enclosed motor with augmented cooling by means of a separately-driven fan blowing external air over the cooling surfaces and /or through the cooling passages, if any, incorporated in the motor


• A totally-enclosed water or other liquid-cooled motor (TEWC) is a totally-enclosed motor with augmented cooling by means of water or other liquid-cooled surfaces embodied in the motor itself.

26Special consideration during design

• Class F insulation

• Non-sparking brass shaft slingers

• Oversized conduit box with threaded conduit holes

• Wires connection sealed in Chico compound

• Non-sparking, corrosion resistant cooling fans

27Special consideration during design

• Cast iron end plates and fan covers

• Stainless steel breathers and drains

• Low-loss steel laminations for higher efficiency

• Precision dynamic balancing

• High temperature polyester varnish impregnated armatures

28Choice of System between IS and FLP

• For coal mines no choice exists, since by regulations all signal and telephone systems must be intrinsically safe.

• In industrial applications, especially where working conditions are good, supervision informed and responsible, and inspection and maintenance meticulous, FLP will permit freer use of automatic telephone systems.

29Choice of System between IS and FLP

• FLP equipment can only be certified for gases in Groups I, II and Ill, and its use is not permitted with gases of Group IV. Intrinsically safe equipment can however be certified for use in certain gases in Group IV.

• As motors operate at high voltage, explosion proof is the only protection mechanism, not intrinsic safety.

30Conclusion

The explosion-proof protection method is the most widely known, and has been used in applications for the longest period of time. However, it is generally agreed that the intrinsic safety protection method is safer, more flexible and costs less to install and maintain. Certified devices could have a combination of the two.

31References

1. http://www.nema7.com/uploads/cms_uploads/2016/07/hcl-explosion-proof-andintrin-1468600120.pdf

2. http://www.pepperl-fuchs.us/usa/downloads_USA/explosion-protection-and-intrinsicsafety-101.pdf

3. http://www.esi-tec.com/blog-pressure-sensors-transmitter-transducer/2013/09/whatis-intrinsic-safetypressuretransmitters

4. http://www.mtlinst.com/images/uploads/datasheets/App_Notes/AN9003.pdf

5. http://abhisam.com/downloads/white-papers/intrinsic-safety-how-it-works/

http://www.nema7.com/uploads/cms_uploads/2016/07/hcl-explosion-proof-andintrin-1468600120.pdf




http://www.pepperl-fuchs.us/usa/downloads_USA/explosion-protection-and-intrinsicsafety-101.pdf




http://www.esi-tec.com/blog-pressure-sensors-transmitter-transducer/2013/09/whatis-intrinsic-safetypressuretransmitters




http://www.mtlinst.com/images/uploads/datasheets/App_Notes/AN9003.pdf



http://abhisam.com/downloads/white-papers/intrinsic-safety-how-it-works/



32RESEARCH AND DEVELOPMENT ON

EXPLOSION AND PREVENTION OF EXPLOSIONS IN MINES

33Overview

• EXPLOSION• Mechanism of Explosion• Types of Explosions• PREVENTION OF EXPLOSIONS• Explosion Protection Plan• Explosion Control Measures• References

34EXPLOSION

• In coal mines there are hazards that are inherent to the coal seam and those that are introduced by the mining method.

• One of the most devastating events that can occur in a mine is an explosion.

35EXPLOSION

• An explosion is a rapid increase in volume and release of energy in an extreme manner, usually with the generation of high temperatures and the release of gases.

• Having an explosion underground can result in the loss of personnel and the loss of the mine itself or a significant portion of it

36Mechanism of explosion

For an explosion to occur four main elements must coexist. These are• Fuel

• Oxygen• Energy source

• Chemical chain reaction.


Fuel• The most common fuel sources for explosions in

underground mines are flammable gases and explosive dust.

• In coal mining flammable gases can be present as a seam gas, or produced as a result of oxidation or distillation of coal.• The extraction process can generate fine coal dust that

could provide sufficient fuel for an explosion.


Oxygen

Ventilation air is supplied to the mine to support life, provide oxygen for internal combustion engines, dilute and render gases harmless and to provide comfortable working environments by removing heat, dust and humidity.

An airflow between 7 and 20 m3 /s with an emission of 1000 l/s would create an explosive mixture.


Energy source

The energy sources that are found in and around mines are numerous. They are

• Diesel and Mechanical equipment

• Explosives

• Electrical infrastructure and equipment

• Frictional ignitions


Chemical Chain Reaction

The effects of changing pressure on the auto-ignition temperature and the widening of the flammable range with elevated temperatures. These relate to the continuance of a chemical chain reaction that transfers energy throughout the mixture. If the amount of energy that is transferred into the adjoining unreacted mixture is insufficient, then the reaction will cease in that direction even though it may be within the flammable range.


The above fuels, ignition sources and airflows can, in the right condition of coexistence, form a flammable or explosive atmosphere. If undetected, the by-products of fire may be carried throughout the mine or tunnel workings, creating the potential for a deadly atmosphere – either not fit for respiration, or explosive, or both.

42Types of Explosions

Explosion in mines can be of three types:• Methane explosion• Coal dust explosion• Water gas explosion (rare)

43Methane Explosion

Methane forms in coal seams as the result of chemical reactions taking place when the coal was buried at depth. Methane occurs in much higher concentrations in coal than other rock types because of the adsorption process, which enables methane molecules to be packed into the coal interstices (gaps or spaces) to a density almost resembling that of a liquid.

44Methane Explosion

• Methane is flammable when mixed with oxygen in a wide range of concentrations, but generally between 5-15% methane in air by volume.

• The auto ignition temperature of methane is 537°C.

45Methane Explosion

Methane explosions are characterized by two distinct operations: • Direct blast• In direct blast, a pressure wave of great force and speed

travels ahead of explosion flame.

• Back lash• The back lash is caused by vacuum arising out of cooling of

explosion gases and condensation of water vapor and is of less intensity than direct blast but traverses the same path backward.

46Coal Dust Explosion

• Coal dust is finely divided matter smaller than 100 micrometer (µm) and of low mass. It can remain suspended in air for a relatively long time and is hazardous because it can be carried through the ventilation system for hundreds of meters, gradually falling out at various places along roadways and workings.


• In a methane explosion, if enough wind pressure is created, the coal dust is raised into the air and re-distributed, potentially igniting a more deadly secondary coal dust explosion.

• For a coal dust explosion to take place in mines, two conditions must be fulfilled.


The dust is present as dense cloud and a source of ignition in the form of flame must be present. The maximum flame temperature at stoichiometric composition is about 2500 0K. In practice it varies from 800-1000 0C. Maximum explosion pressure upto 7 bars possible.

49Conditions for Coal Dust explosion

• A combustible dust• The dust is suspended in the air at a proper concentration• oxidant• The dust should be confined• Ignition source• If any of these five conditions is missing there can be no

dust explosion

50Ignition Criteria for Coal Dust Explosion

• Burning Embers and Agglomerates• Self-Heating• Impact/Friction

• Electrical Equipment• Firedamp explosions

51Factors affecting coal dust explosion

• Particle size

• Dustiness of Mine Working

• Volatile matter

• Percentage of ash, moisture, fire damp

• Oxygen concentration

• Nature and intensity of ignition source

52Prevention of Explosions

EXPLOSION PROTECTION PLAN

The fire and explosion risk assessment process will have identified the potential fire and explosion hazards present, the risks they give rise to, and the measures neces.sary to avoid and control those risks

53EXPLOSION PROTECTION PLAN

The explosion protection plan required by regulation 4 of The Mines Miscellaneous Health and Safety Provisions Regulations 1995 will need to set out those measures to be taken:

• To prevent an explosive atmosphere occurring

• To exclude, or control, potential sources of ignition;


• In the event of an explosive atmosphere of any type occurring or where the concentrations of flammable gas in the mine air exceed legal limits

• To mitigate the consequences if an explosion occurs.


• The measures which will need to be set out in the plan may include:

• Firedamp drainage arrangements to control emissions of firedamp from the strata and waste areas

• Ventilation arrangements (both main and auxiliary) to control the level of firedamp in the atmosphere and prevent explosive atmospheres occurring


• Arrangements for monitoring and detection of dangerous levels of firedamp by the use of portable automatic firedamp detectors at suitable places

• Arrangements for automatically cutting off power supplies to equipment in singleentries should the auxiliary ventilation system fail

57EXPLOSION CONTROL MEASURES

• These fall into six broad categories:

• Zoning of the workplace

• Selection of suitable equipment

• The prevention of explosive atmospheres


• De-energizing equipment in explosive or potentially explosive atmospheres

• The control of other ignition sources

• Degassing operations


Zoning

zoning is the only basis from which they can identify equipment appropriate for use in particular circumstances. The zones where different types of explosive atmospheres (gas, dust, vapor or mist) could occur may not be the same and may not even overlap, so it will be necessary to zone for each type of potential explosive atmosphere.


The selection of suitable equipment

• The categories of the explosion protected equipment

• The way these categories are to be used in ‘explosive’ and ‘potentially explosive’ atmospheres

• The explosive atmosphere being formed by either gas, mist, vapor and/or flammable dust under normal atmospheric conditions

• The type of explosion protected equipment


Equipment for use in explosive atmospheres below ground

When an explosive atmosphere of any kind exists, only Category M1 equipment, or equipment previously approved to remain energized, is permitted because of its very high level of protection.

While cap lamps are categorized as category M2, a mines rescue team could be allowed to wear them in an explosive atmosphere for a short period of time to save life


Equipment for use in potentially explosive atmospheres below ground

Where a potentially explosive atmosphere exists, both M1 and M2 equipment and their equivalents may be used.


Preventing an explosive atmosphere occurring

The principal measures to prevent the build-up of an explosive atmosphere are:

• Ventilation systems (including local exhaust ventilation systems) for explosive gas, mist and vapor atmospheres

• Firedamp drainage for explosive gas atmospheres


• Removing flammable dust from the mine, or consolidating it so that it cannot be raised into the air

• Where flammable dust is likely to settle, maintaining a sufficient proportion of incombustible dust in mine roadways such that an explosive dust atmosphere will not occur if it is raised into the air.


De-energizing equipment used in potentially explosive atmospheres in mines

If the concentration of firedamp in the general body of mine air exceeds 1.25% the only electrical equipment that should remain energized is that which is both safe for use in an explosive atmosphere and is necessary to secure the safety of people in the mine, including their escape and rescue.


The Equipment and Protective Systems Intended for Use in Potentially Explosive Atmospheres Regulations 1996 require all category M2 equipment, both electrical and nonelectrical, to be deenergized when the atmosphere changes from being potentially explosive to explosive.


Control of other ignition sources

Naked lights

Section 62 of The Mines and Quarries Act 1954 prohibits the use of lights other than permitted lights in all mines where there is a risk of an explosive atmosphere occurring, and section 67 prohibits the use in such mines of equipment designed or adapted to produce an unprotected flame or spark.


Where there are frictional ignition risks owners and managers will need to take appropriate preventative and protective measures including:

• Adequate ventilation

• Water ignition suppression systems, such as pick-back-flushing

• Equipment design - certain types of picks and pick configurations are less likely to produce incentive sparks than others.


Degassing operations

Mine owners and managers should design the mine layout, drivage sequence and mining systems to minimize the opportunity for dangerous concentrations of flammable gas to accumulate and avoid the need to degas. Managers should in particular avoid unventilated single entries and, in seams where an explosive atmosphere will form quickly, to have standby systems, such as venturi, that operate if the auxiliary fan(s) stop

70References

• https://www.business.govt.nz/worksafe/information-guidance/all-guidance-items/fire-orexplosion-in-underground-mines-and-tunnels/acop-fire-explosion-mines-tunnels-pdf• http://

www.mineaccidents.com.au/uploads/explosion-case-study.pdf• http://www.hse.gov.uk/mining/feguidance.pdf

https://www.business.govt.nz/worksafe/information-guidance/all-guidance-items/fire-orexplosion-in-underground-mines-and-tunnels/acop-fire-explosion-mines-tunnels-pdf





http://www.mineaccidents.com.au/uploads/explosion-case-study.pdf




http://www.hse.gov.uk/mining/feguidance.pdf



Engineering

Intrinsic safety and flameproof apparatus in mines