1RESEARCH AND DEVELOPMENT ON

EXPLOSION AND PREVENTION OF EXPLOSIONS IN MINES

MINE ENVIRONMENT ENGINEERINGMN331 ASSIGNMENT-1

Presented byPATI JAYA CHANDRA

113MN0480GROUP-1

2Overview

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

3EXPLOSION

• 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.

4EXPLOSION

• 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

5Mechanism of explosion

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

• Oxygen• Energy source

• Chemical chain reaction.

6Mechanism of explosion

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.

7Mechanism of 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.

8Mechanism of explosion

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

9Mechanism of explosion

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.

10Mechanism of explosion

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.

11Types of Explosions

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

12Methane 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.

13Methane 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.

14Methane 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.

15Coal 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.

16Coal 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.

17Coal 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.

18Conditions 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

19Ignition Criteria for Coal Dust Explosion

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

• Electrical Equipment• Firedamp explosions

20Factors 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

21Prevention 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

22EXPLOSION 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;

23EXPLOSION PROTECTION PLAN

• 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.

24EXPLOSION PROTECTION PLAN

• 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

25EXPLOSION PROTECTION PLAN

• 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

26EXPLOSION CONTROL MEASURES

• These fall into six broad categories:

• Zoning of the workplace

• Selection of suitable equipment

• The prevention of explosive atmospheres

27EXPLOSION CONTROL MEASURES

• De-energizing equipment in explosive or potentially explosive atmospheres

• The control of other ignition sources

• Degassing operations

28EXPLOSION CONTROL MEASURES

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.

29EXPLOSION CONTROL MEASURES

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

30EXPLOSION CONTROL MEASURES

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

31EXPLOSION CONTROL MEASURES

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.

32EXPLOSION CONTROL MEASURES

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

33EXPLOSION CONTROL MEASURES

• 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.

34EXPLOSION CONTROL MEASURES

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.

35EXPLOSION CONTROL MEASURES

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.

36EXPLOSION CONTROL MEASURES

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.

37EXPLOSION CONTROL MEASURES

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.

38EXPLOSION CONTROL MEASURES

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

39References

• 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