Science and Current Events:

Crandall Canyon and Underground Coal Mining in Utah

Lesson by: Nathan Armstrong
Questions or suggestions email: nathan.armstrong@utah.edu

Time:

45 min

Grade:

7th and 8th

Curriculum included in this lesson:

Science – 7th Grade

• Standard 2 – Students will understand the relationship between properties of matter and Earth’s structure.

PreEngineering

• Standard 1 – Nature and scope of Engineering.
• Standard 2 – Creative problem solving
• Standard 3 – Communication

Specific topics covered in this lesson:

• Volume
• Density
• Rock Strength
• Metric and English units
• Underground coal mining
• What mining engineers do in their careers
• Mine economics
• Decision making

Note: When appropriate, it should be discussed that Engineers in the US use English units such as pound and foot. Elsewhere in the world, metric, or SI, units such as kilogram and meter are used. Engineers should be proficient in the use of both and be able to convert back and forth. Units for this lesson are given English with metric in parentheses.

As preparation for this lesson, it might be good to have the students read an article in the paper about the Crandall Canyon mine to introduce them to the lesson. Two articles are attached with this lesson. Others can be found via an article search on the internet.

Introduction to Coal

What is it?

• Coal is a sedimentary rock formed from compaction of fossilized organic matter. It is a fossil fuel.

What is coal used for?

• Coal is mostly used to produce energy.
• It is burned to heat water. The water turns to steam which turns electric generators which produce energy.
• It is also used in the steel making process.

How do we get coal?

• Coal must be mined.
• In Utah, it is found deep underground, so shafts and tunnels must be dug to access the coal.
• In other states such as Wyoming and West Virginia, coal is near the surface, so the top dirt layer can be stripped away, and the coal taken out.

An educational slide show on coal for more information can be downloaded from the following site:
www.rmcmi.org At the bottom left of the homepage, there is a link to an educational slide show.

Coal properties compared to other materials:

Coal types vary but it is not a very dense rock. It is generally brittle and some samples could be broken easily just by dropping them. They could even broken by your bare hands.

For this part of the lesson, common Utah rock samples can be used to give the students an idea of how coal compares to other Utah rocks such as limestone and granite. Have some volunteer students come up and handle the samples and explain to the class what properties they observe. For reference, pictures of these samples are below:

Coal

Granite

Limestone

Densities for comparison:

• Coal: 93.6 lb/ft3 (1500 kg/m3)
• Limestone: 176.6 lb/ft3 (2830 kg/m3)
• Granite: 171.6 lb/ft3 (2750 kg/m3)
• Air(sea level): 0.0749 lb/ft3 (1.2 kg/m3)
• Water: 62.4 lb/ft3 (1000 kg/m3)

What are the dangers in an underground coal mine?

• Unstable roof
  • The roof must be supported.
• No light
  • Miners must use electric headlamps.
• No water
  • Clean water must be piped into the mine.
• No food
  • Food must be brought in and stored in a safe place.
• Bad air
  • Poisonous gases include carbon monoxide, methane, and sulfur dioxide.
  • Clean air must be circulated via fans (can be 12 ft diameter fans) through ventilation shafts.
  • Miners carry self rescuers (a breathing apparatus) that can convert deadly carbon monoxide into relatively harmless carbon dioxide for one hour, with the idea a miner should be able to get to safety within that time.
• Communication
  • The mine needs to be specially wired to get radios to work.

How do these dangers increase in an emergency such as a fire or roof collapse?

• Supplies can be cut off.
• Communication can go down.
• There might be some confusion.
• Bad air begins to build up, especially if there is a fire.

For further discussion, the students can be encouraged to think of ways safety can be improved in underground coal mining.

As an example, if there were a better way to communicate with the trapped miners, their location might have been ascertained sooner and hence a better rescue plan might have been devised.

How is coal mined in Utah?

There are two popular ways: longwall mining, and room and pillar mining. Room and Pillar is discussed here.

Room and Pillar Mining

At the Crandall Canyon mine, a 10 ft (3 m) coal seam was being mine 1500 ft (457 m) underground. For comparison, the Empire State Building is 1472 ft (449 m) from the ground to the top spire. The tallest building in Salt Lake City is the Wells Fargo Building which stands 423 ft (129 m) high. Working at this underground mine would be like working on the bottom floor of the Empire State building with all that weight on top. Without support, it would collapse. That is why room and pillar mining is used. The rooms are where the coal is taken out, and the pillars are left to support the weight of the overburden (all the rock between the coal and the surface). The more overburden the bigger the pillars have to be.

Below is a sample schematic of a room and pillar mine that can be shown or drawn on the board. The dimensions given are just an example. The exact dimensions of the rooms and pillars at Crandall Canyon or other underground mines may vary. Units are in feet.

As an example:
A coal pillar might be 100 ft (30 m) x 100 ft (30 m). The rooms (or entries and crosscuts as they are referred to) are 20 ft (6 m) wide. A pillar in a mine with these dimensions located 1500 ft (457 m) underground would need to be able to support 3 billion pounds (1.4 billion kilograms) or 1.5 million tons (1.4 million metric tons).
These pillars are able to offer that much support. But once they are removed, the support is gone.
Why would you want to remove the pillars?
Keep in mind that the pillars are composed entirely of coal. Coal is worth money. In the above example, if the pillars are left, only 31% of the coal is removed. There is still a lot of coal left in the pillars. How much?
Using the same numbers from the above example the value can be calculated (this calculation may be beyond the scope of the class, the important number for the students to understand is the value of one coal pillar):
Volume of the pillar is 100 ft*100 ft*10 ft (30 m*30 m*3 m) = 100000 ft3 (2700 m3)
Mass of the pillar is volume*density
(100000 ft3*93.6 lb/ft3) / 2000 lb/ton = 4680 tons
(2700 m3*1500 kg/m3) / 1000 kg/mton = 4050 mtons (conversion is an estimate)
Price at the time of the Crandall Canyon mine disaster was $35 per ton ($40 per mton) of coal. Current prices can be found at the following website:
www.eia.doe.gov/fuelcoal.html
Find the link for spot prices. Utah coal is considered Uintah Basin Coal. Each coal mine contracts for its own prices, so these are just averages for the area.
The value of one coal pillar is therefore:
4680 tons * $35 per ton = $163,800 (4050 mtons * $40 per ton = $162,000)
There may be hundreds of pillars in one section of a coal mine. So the value of coal left in the pillars is in the millions of dollars.

What can you buy for $163,000?

What can you buy for $16 million?

To make a profit and pay the miners, coal must be removed. Pillar retreat mining is where they work from the back and start removing pillars. They retreat towards the entrance as the roof begins to collapse. This can be done relatively safe if pillars are removed in the correct order, and enough pillars are left to offer just enough support for retreat. It is very dangerous but also very profitable. Adverse ground conditions such as faults make it even more risky.

How do mine engineers and mine managers decide how many pillars to remove?

How would the students decide?

There is great profit, but if there is an accident, what is the . long term cost. The Crandall Canyon mine was shut down. There are insurance, fines, and legal fees to pay. Not to mention the grief of a community.

What is the cost of a coal miner?

Activity: “Pillar Retreat Jenga”

Students are split into groups. They are not competing against each other; rather, they are competing against the other groups. The group that can safely remove the most coal is the winner. The jenga game is used to represent a coal pillar. The students, as a group, are asked to remove as many jenga blocks, which represent coal, as they can. The catch is, on two sides of the jenga pillar, there is a coal miner (I used army men). If the pillar falls and lands on a coal miner, they are disqualified. They can stop at any time, but after that, no more mining is allowed. If real coal pillar dimensions were applied to a jenga block, then one block would be worth about $5000. A sample photo of how I set the game up is below.

Questions to have the groups think about as they “mine”:

• Can you predict which way the tower is going to fall (before mining, after mining for a few minutes)?
• How are you going to decide when to stop?
• Who gets to make the final decision, or is it by majority vote?
• When have you made enough money?
• Why should you stop mining before the pillar actually fails?
• How hard is it to stop mining when the coal is worth so much?