Intrinsic safety and flameproof apparatus in mines

MINE ENVIRONMENT ENGINEERING
ASSIGNMENT-1 MN331
Presented by
PATI JAYA CHANDRA
113MN0480
GROUP-1
1

INTRINSIC SAFETY AND
FLAMEPROOF APPARATUS
IN MINES 2

OVERVIEW
• 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
3

What 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
4

What 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.
5

Intrinsic 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.
6

• 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.
7

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
8

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.
9

• 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.
10

Advantages 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
11

• 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
12

• 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.
13

Disadvantages 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.
14

FLAME 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.
15

FLAME 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.
16

British 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
17

British 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.
18

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
19

Statutory 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.
20

Statutory 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.
21

IS 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
22

FLAMEPROOF 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.
23

• 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 sur-
faces and /or through the cooling passages, if any, incorporated in
the motor
24

• 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.
25

Special 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
26

Special 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
27

Choice 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.
28

Choice 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.
29

Conclusion
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.
30

References
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/
31

RESEARCH AND DEVELOPMENT ON
EXPLOSION AND PREVENTION OF
EXPLOSIONS IN MINES
32

Overview
• EXPLOSION
• Mechanism of Explosion
• Types of Explosions
• PREVENTION OF EXPLOSIONS
• Explosion Protection Plan
• Explosion Control Measures
• References
33

EXPLOSION
• 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.
34

EXPLOSION
• 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
35

Mechanism of explosion
For an explosion to occur four main elements must coexist. These
are
• Fuel
• Oxygen
• Energy source
• Chemical chain reaction.
36

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.
37

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.
38

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
39

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.
40

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.
41

Types of Explosions
Explosion in mines can be of three types:
• Methane explosion
• Coal dust explosion
• Water gas explosion (rare)
42

Methane 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.
43

Methane 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.
44

Methane 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.
45

Coal 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.
46

Coal Dust Explosion
• 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.
47

Coal Dust Explosion
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.
48

Conditions 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
49

Ignition Criteria for Coal Dust Explosion
• Burning Embers and Agglomerates
• Self-Heating
• Impact/Friction
• Electrical Equipment
• Firedamp explosions
50

Factors 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
51

Prevention 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
52

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;
53

• 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.
54

• 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
55

• 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
56

EXPLOSION CONTROL MEASURES
• These fall into six broad categories:
• Zoning of the workplace
• Selection of suitable equipment
• The prevention of explosive atmospheres
57

• De-energizing equipment in explosive or potentially explosive
atmospheres
• The control of other ignition sources
• Degassing operations
58

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.
59

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
60

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
61

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.
62

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
63

• 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.
64

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.
65

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.
66

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.
67

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.
68

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
69

References
• 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
70

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