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The Underground Coal Mine Blast Accident & How To Prevent It

INTRODUCTION
The world primary energy consumption is getting high from year to year. In this year (2005), the world primary energy consumption is predicted around 11,063 million TOE, in which around 21,8% of them (2,409 million TOE) is supplied by coal. In the next 2010, the world consumption is predicted will jump to 12,413 million TOE, in which 21,3% of them (2.638 million TOE) will be supplied by coal (EIA, International Energy Outlook, 2002
). Still based on the information from EIA, in the year of 2002, especially for Asia region, the coal consumption of China People Republic will increase from year to year, including for their preparation as the Olympic host in the next 2008. The detail data about the world primary energy consumption is attached on Table-1.

The primary energy consumption in Asia region, as a big population region, is getting high from year to year. China, as the biggest population country in this region, is predicted will use coal as it’s main energy. In 1999, China consummated around 1,595.5 million TOE. In the next 2010 and 2020, China as the biggest country in Asia region will consummate around 2,757.2 and 4,193.1 million TOE of the world primary energy. Around 60% of them will be supplied by coal energy which is produced by the country and by another countries in the region, including Indonesia.

Mainly, the coal can be mined through two different ways of mining; the Surface Coal Mining (SCM) and the Underground Coal Mining (UCM). Currently, the SCM that has been implemented for hundred of years, is getting un-popular. It is in relation to the improvement of people concern to the environmental protection issues. The UCM is claimed as the best method of mining in relation to the environmental protection issues. But unfortunately, this mining method has a very high risk to employees’ accident.

UCM methods have been introduced many years ago in Indonesia but this method of mining is not as popular as Surface Coal Mining (SCM). PT. Arutmin Indonesia, as one of the three biggest coal mining company in Indonesia, has four surface coal mining sites, i.e. Satui, Asam-Asam, Senakin and Batulicin Coal Mine Sites. UCM has been newly introduced at Satui Coal Mine site – in South Kalimantan and is the only one operating in the region.

SCM methods are developed by digging the overburden materials and taking out the coal from the earth. These type of mining are limited by an economical “Stripping Ratio”, such as 5:1.


These mining methods can potentially have serious impacts to the environment surrounding the mining area. Compared to the SCM Method, UCM Methods have minimum impact to the environment. But unfortunately, this mining method has a higher risk or impact for people who working at the UCM. Until now, a lot of people are still killed in the UCM area. For example, on 26 April 1942, 1,527 employees are killed in Honkeikou–China.

CHARACTERISTICS OF UNDERGROUND COAL MINING
Compared to the SCM methods, the UCM methods have some characteristics or limitation as follows:
1. As their name, the UCM methods are developed in the underground area. In some cases, these type of mining methods can be developed for thousands of meters into the earth.

2. They have a limitation in free air circulation, especially for oxygen gas circulation required for employees’ breathing who are working in the underground panel.

3. They have a limitation in lighting, causing almost all tunnels and work panels are extremely dark. This condition can impact the employees’ sight who are working there.

4. Limitation in working area for employees’ and equipment movement. This condition has potential problem for increasing of employees’ hit, pinched and scratch accidents.

5. The UCM methods are affected by the earth warming effect. More deeper more warmer. This effect is strongly felt by the employees when the underground ventilation system is not working properly.

6. They are also affected by the earth’ tension effect. That’s why the underground tunnels should be maintained regularly to minimize the impact of the effect to the tunnels. Otherwise the tunnels will be narrower.

7. These type of mining methods also have a risk of roof falling. If the tunnel and/or the working panel collapse, it could kill employees working in the area. This accident has potential to stop air circulation to other working panels. We can imagine when people working without fresh air (oxygen).

8. The UCM methods also have a high risk of water flooding. Underground water from around can enter any empty spaces of the underground coal mining area.

9. Some types of hazardous gases can also enter and be able trapped in the UCM spaces. The hazardous gases will decrease the oxygen availability and will impact to the employees’ health and/or safety.

10. Last but not least, the UCM methods have a high risk on the circulation of coal and/or stone dust.

ACCIDENT RISKS IN UNDERGROUND COAL MINING
Some characteristics of the UCM have potential risk to cause accidents and/or health impacts to their employees. Some kinds of underground accident risks that can occur at an UCM are:  a. Mine blast accident risk,
b. Mine fire accident risk,
c. Hazardous gas circulation risk;
d. Coal and/or stone dust circulation risk;
e. Mine flood accident risk;
f. Mine fall / collapse accident risk; and
g. Other general accident risks, such as pinched, scratched, hit, etc.

This paper will only discuss about the underground mine blast accident risk. Until now, it is the highest accident risk at the UCM. This risk has great concern and challenges to be managed properly to ensure a safer UCM area.

UNDERGROUND COAL MINE BLAST ACCIDENT
Methane gas and/or coal dust in underground coal mining has potential risk causing blasting accident at the underground coal mining. Methane gas has some characteristics, such as:
a. Has no color,
b. Has no taste,
c. Has no smell, and
d. Toxic.
This gas has type weight = around 0.56. It means the weight is lighter than air. That is why the gas is usually trapped on the ceiling of the UCM, especially at the curve areas. This gas has possibility to blast at concentration of 5% ~ 15%. At concentration of 9.5%, this gas is easily to blast.


Coal dust, which easily to be found at coal transportation facility areas in panel and tunnel areas, has specific characteristic; i.e. easily to fire and blast. The coal dust which produced at work panel areas, at coal seam tunnels and at UCM transportation facilities, has been proofed as a factor causing UCM blasting accident that have killed a lot of the UCM employees around the world.

On the next table, we can see how many employees had been killed by the UCM blast accident around the world, especially those which have killed more than 300 employees in each accident.

Table 1.
Fatality in Underground Coal Mining around the World
(more than 300 victims)
COUNTRY
COMPANY
DATE OF ACC.
TOTAL FATALITY
British
Ox
December 12, 1886
361
French
Coullier
March 10, 1906
1,099
Japan
Takashima
March 28, 1906
307
Japan
Toyokoku
July 20, 1907
365
British
Monoger
December 6, 1907
361
Germany
Lad Bold
November 12, 1908
360
British
Pretoria
December 21, 1910
344
British
Senghenice
December 18, 1913
439
Japan
Wakanabe
November 28, 1914
423
Japan
Usui
December 1, 1914
422
Japan
Houjou
December 25, 1914
687
China
Bujun Daisan Kou
January 11, 1917
917
Japan
Onoura
December 21, 1917
369
China
Kai
October 14, 1920
431
China
Sei
May 22, 1940
341
China
Honkeikou
April 26, 1942
1,527
China
Seian Taishin Dai Ikkou
October 11, 1942
310
Germany
Luizendal
N/A
300
Japan
Mike
November 9, 1963
453
Source: “Underground Mining & Safety Technology” training handbook released by Ikeshima – Nagasaki Training Center – Japan.

HOW TO PREVENT UNDERGROUND COAL MINE BLAST ACCIDENT
As previously concerned; by knowing the characteristics and the accident risks of underground coal mining, we can use this as a challenge to improve underground safety performance by reducing any kinds of accidents in these areas, including UCM blast accidents.

The “Fire Triangle” concept is typically used to prevent UCM blast accidents.

Based on the above concept, we can prevent UCM blast accidents by:
a. Monitoring and handling of fire flame / ignition;
b. Monitoring and handling of explosive / flammable materials (such as methane gas, coal dust, etc); and
c. Managing oxygen gas.

Monitoring & handling fire flame / ignition
There are some kinds of fire flame/ignition sources in underground coal mine areas, such as:
a. Blasting activities,
b. Electrical equipment / installation,
c. Safety / head lamps,
d. Cigarettes / matches,
e. Mine fire / self combustion, and
f. Other sources.

Based on the flame / ignition sources, we can organize some activities to prevent the UCM blast accidents, as follows:
Blasting activities
Implement good ucm blasting permit
Electrical equipment/installation
Use flame-proof electrical equipment
Safety / head lamps
Conduct pre-start checking prior to use the lamps
Cigarettes /matches
Organize personal check to employees and/or guests who want to enter the underground coal mine
Mine fir or self combustion
Install permanent CO gas detector
Install automatic fire fighting equipment
Other sources
Install “No Flame / Ignition” sign
Organize Safe Behavior Observation
Install “Centralized Monitoring System”
Install “Water Pockets” in some designated tunnels.


Monitoring & handling of explosive materials
Explosive materials in UCM could be:
a. Methane gas (CH4)
b. Coal dust.
In relation to monitoring and handling of the explosive materials, some efforts to prevent UCM blast accidents are as follows:
a. Install methane gas detector
b. Drain the trapped methane gas
c. Spraying road header or drum cutter (equipment) with water
d. Spraying of UCM tunnels with limestone dust
e. Concreting of UCM tunnels


a. Regular maintenance/ cleaning areas under conveyors and other hazardous areas
b. Install CO gas detector and monitoring system.

Managing oxygen gas
Some efforts to prevent the UCM blast accidents could be conducted by managing the oxygen gas circulation in the underground coal mine, such as follows:
a. Increase the oxygen gas supply to where the methane gas is trapped to decrease the methane gas concentration in that area under it’s explosion point. The explosion point of methane gas is between 5 to 15%. Install “wind doors” and/or “wind bridges” to increase or decrease the oxygen supply to designated areas.
b. Stop the oxygen gas supply to where the explosion has happened, by blocking the blasted / fired areas with concrete blocks. As explained in the “Fire Triangle Concept”, stopping the oxygen gas supply will stop the coal fire / blast.


CONCLUSION
Based on the previous explanations, there are some conclusions that can be drawn:
1. The world energy consumption for coal is getting higher from year to year.
2. Coal can be mined through surface or underground coal mining methods.
3. The underground coal mining method has some limitations or characteristics.
4. One of the characteristics is the high accident risk of UCM blast.
5. UCM blast accident has occurred hundreds of years ago, but until now the accident risk is still high.
6. The principle concept to prevent UCM blast accident is using the “Fire Triangle” concept.
7. Three items of concern with on the “Fire Triangle” concept are; Flame/Ignition, fuel and oxygen.
8. Managing the three items properly will prevent the UCM blast accidents. This type of accident has made thousands of the UCM employees dye.

By:
Ir. Eddy Suprianto, MAppSc. PT Arutmin Indonesia as Safety, Health & Environmental (SHE) Superintendent.


Publication:
HSE Club Indonesia Jurnal 1st Edition, 2006.

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