In the first part of this chapter we looked at how the flame safety lamp was invented and how its main working parts, the gauzes, chimney and glass, protect the flame. But a real lamp is far more than that. It has pillars, a magnetic lock, rings that steer the air, a relighter and even a number plate. This second part covers all of them, along with the safety features, the different types of lamp and the problems that come up in everyday use.
If you have not read the first part yet, start with Flame Safety Lamp: Construction, Parts, Principle and Development. Because the lamp is mainly a gas-testing tool today, we have also linked these notes to our posts on mine gases.
- Safe air speed: the lamp stays alight in air moving up to 15 m/s
- Fuel: petrol or solvent spirit 1425 (or equivalent)
- Wick: round wick only, as per IS:9577-1986
- Types by air entry: top feed, top and under feed, mid feed, under feed
- Relighter lamps: only these are considered suitable for gas testing by sirdars and overmen
- All 21 parts of the lamp
- Safety features and the lantern comparison (Q8 to Q9)
- Rings, gauze metal and the retainer key (Q10 to Q13)
- Magnetic lock and self-extinguishing arrangement (Q14 to Q17)
- Assembly and everyday handling (Q18 to Q27)
- Types of lamp (Q28 to Q31)
- Internal relighter, weight and feeds (Q32 to Q35)
- FAQs
The Complete Parts List
In the previous part we studied parts 1 to 7. Here is the full list of 21 parts, followed by an explanation of parts 8 to 21.
| No. | Part | Main job |
|---|---|---|
| 1 | Bonnet | Protects the gauze and flame |
| 2A | Outer gauze | 20 mesh, the outer layer of protection |
| 2B | Inner gauze | 28 mesh, the main flame arrester |
| 3 | Chimney | Carries hot fumes to the outlet |
| 4 | Small glass | Older lamps only |
| 5 | Large glass | Gives light, shields the flame |
| 6 | Packing rings | Seal the glass joints |
| 7 | Lock (retainer) ring | Holds the glass assembly together |
| 8 | Pillars | Protect the glass from knocks |
| 9 | Oil vessel | Holds fuel and cotton wool |
| 10 | Oil filling hole | Spring-loaded ball or sliding cap |
| 11 | Magnetic lock | Stops unauthorised opening |
| 12A / 12B | Wick / wick tube | Round cotton wick in a round holder |
| 13 | Wick adjusting screw | Raises or lowers the wick |
| 14 | Baffle ring and shut-off ring | Control the air inlet holes |
| 15 | Deflector ring | Turns incoming air towards the wick |
| 16 | Perforated cap | Spreads the outgoing hot air |
| 17 | Inlet holes | Let fresh air in |
| 18 | Outlet holes | Let hot gases and smoke out |
| 19 | Internal relighter | Relights the lamp without opening it |
| 20 | Handle or hook | For carrying and hanging |
| 21 | Number plate or token | Identifies each lamp |
Q7 (continued). Explain the construction and work of each part of the oil safety lamp.
Answer (continued from Part 1):
8. Pillars. These are upright iron rods, about 5 mm thick, that join the bonnet to the oil vessel. They are there to protect the glass. There are five of them for a reason: if a straight rod or stick strikes the lamp, it will hit two pillars and never reach the glass.
9. Oil vessel. Made of brass, it holds enough fuel to burn for roughly 12 to 14 hours. It is packed with cotton wool, which soaks up the fuel so that nothing spills if the lamp falls. The upper edge is threaded so that the bonnet frame can be screwed on.
10. Oil filling hole. A small ball held by a spring closes the filling hole. When oil is pushed in with a filling syringe, the pressure opens the ball. Some lamps, such as the Velox GL-60, have no ball and instead use a washered cap that is slid aside for filling.
11. Magnetic lock. It ties the bonnet to the oil vessel so that nobody can open the lamp in the mine, knowingly or unknowingly. Earlier lamps used a lead rivet lock, but that type is now prohibited by law. How the magnetic lock works is explained in Q14.
12. Wick and wick tube. The wick tube is a round holder cast along with the oil vessel, and the wick hangs from it into the fuel. The wick is a round cotton thread about 6 mm (a quarter of an inch) thick. Lamps once used a flat wick about half an inch wide, but as per Indian Standard IS:9577-1986, only lamps with a round wick are used in mines now. On a flat wick the gas cap looks different from different angles, which can lead to mistakes, and it is also hard to trim it level for a proper testing flame.
13. Wick adjusting screw. This raises or lowers the wick. Modern lamps have a screw at the bottom of the oil vessel that can be turned by hand to make the flame bigger or smaller. Older lamps used a pin, which is now prohibited.
14. Baffle ring and shut-off ring. The baffle ring sits in the lower part of the bonnet and has inlet holes through which air reaches the wick. In bottom-top feed lamps, a shut-off ring above the baffle ring can be turned to close those holes, after which the air enters only through the upper inlet holes.
15. Deflector ring. Placed at roughly half the height of the bonnet, it stops the incoming air from rising straight up and turns it towards the wick, which keeps the flame burning properly.
16. Perforated cap. This is the perforated roof of the bonnet. The air leaves through its holes in several streams, so it does not heat the top of the gauze directly.
17. Inlet holes. The holes that let air into the lamp. If they are at the lower end of the bonnet above the glass, the lamp is called a mid-feed lamp. If air enters through the upper part of the bonnet, the lamp is a top-feed lamp, which allows gas testing right up against the roof. If air enters below the glass, it is a bottom-feed or under-feed lamp. Some designs combine top feed and under feed, and the under-feed holes are closed with the shut-off ring when the lamp is used as a top-feed lamp.
18. Outlet holes. Several holes just under the perforated cap let the hot air and smoke of the lamp escape.
19. Internal relighter. The lamp may go out while a testing flame is being made. The relighter lets you light it again without opening it. A filament wire in front of the wick gets current from dry cells (two 1.5 V cells) fitted in the oil vessel, and the glowing filament lights the wick. More in Q32.
20. Handle or hook. Used for carrying and hanging the lamp.
21. Lamp number or token. By law every lamp must carry a number. It is either engraved on a number plate on the bonnet or fixed to the hook as a separate token. If an accident happens, this tells you who was issued the lamp, and it keeps the lamp records in order.
Safety Features of the Lamp
Q8. What are the safety arrangements of a flame safety lamp?
Answer: The lamp has several built-in safety arrangements:
- Two gauzes. They take heat from the hot fumes of the flame and spread it, so the gases leaving the gauze are cooler than the ignition temperature of the methane outside. The layer of burnt gases (carbon dioxide) between the two gauzes separates the incoming firedamp-laden air from the hot fumes inside, giving extra protection.
- Bonnet. It protects the gauze from outside blows and the flame from strong air currents. The lamp does not go out even in air moving at up to 15 m/s.
- Two asbestos packing rings above and below the glass keep hot gases and fumes from leaking out.
- Magnetic lock prevents anyone from opening the lamp in the mine without authority.
- Strong glass that does not break in a gas explosion inside the lamp, or if the lamp is dropped.
- Five pillars shield the glass from external blows.
- The metal of the lamp is strong, does not produce sparks if it is scraped against stone, and spreads the heat of the flame quickly.
Q9. What is the difference between a lantern (ordinary oil lamp) and an oil safety lamp?
Answer:
| Point | Oil safety lamp | Ordinary lantern |
|---|---|---|
| Hot gases | Two gauzes cool the hot gases so they cannot light the gas outside | Hot gases go straight out, which is dangerous where gas is present |
| Strength | Strong metal (steel or brass), tough glass, pillars to protect the glass, bonnet to protect the gauze | Thin tin body and weak glass that cracks with heat, a gas explosion or a small knock |
| Flame escape | Packing rings and magnetic lock prevent the flame escaping | No such arrangement |
| Filling | Filling is arranged so that fuel does not spill | Fuel can spill and cause a fire if overturned or tilted |
| Low oxygen | Burns down to about 17 percent oxygen, then the wick goes out and warns of danger | Burns even below 17 percent, so there is no warning of oxygen deficiency |
The last row matters in practice. A lamp that stays alight when oxygen drops, as a lantern does, hides the danger. For more about the gases involved, see our mine gases posts, including firedamp.
Rings, Gauze Metal and the Retainer Key
Q10. How many rings are there in a top-feed safety lamp?
Answer: A top-feed lamp has five kinds of rings: (1) the deflector ring, (2) the baffle ring, (3) the shut-off ring, (4) the glass retainer (lock) ring and (5) two asbestos packing rings, one above and one below the glass.
Q11. What metal is the retainer ring made of?
Answer: The retainer ring is made of brass.
Q12. Copper conducts heat better than iron. Why is the gauze made of iron wire instead of copper wire?
Answer: It is true that copper conducts heat better than iron, and a copper gauze would spread the heat even better. But copper gauzes burn out and get damaged quickly, and they are expensive, so they are not used.
About 40 to 50 years ago, surveyors' lamps did have copper gauzes so that they would not disturb the compass. The instruments surveyors use now do not need that, so no mine uses a lamp with a copper gauze today.
Q13. How is the glass retainer ring opened?
Answer: With a special key that has two pointed prongs. The prongs fit into the notches in the retainer ring so that it can be turned.
Magnetic Lock and Self-Extinguishing Arrangement
Q14. How does the magnetic lock work?
Answer: Ratchet teeth are cut on the upper face of the oil vessel. When the lamp is put together, a steel bolt called a pawl slips over the teeth. But when someone tries to turn the vessel the other way to open it, the pawl jams in the gap between the teeth, so the oil vessel cannot be separated from the bonnet.
To open the lamp, it is placed in the lamp room over an electromagnet, so that the pawl comes right above the magnet. The magnet pulls the pawl up and out of the teeth, and the oil vessel can then be unscrewed.
Q15. Why are two gauzes used in a safety lamp?
Answer: The smoke and carbon dioxide formed inside the lamp fill the gap between the two gauzes and separate the mine air from the air inside the lamp. This is extra protection, and it is the reason the French engineer Marsaut began using two gauzes. In addition, if one gauze develops a fault, the other still protects, so the safety is doubled.
Q16. How is the self-extinguishing arrangement provided in a safety lamp?
Answer: If someone opens a lamp in the mine without knowing the danger, it can be risky, which is why the lamp has a magnetic lock. A newer arrangement goes one step further: after the magnetic lock is released and the oil vessel is turned to open it, the flame goes out progressively. So the lamp cannot be opened without putting out the flame.
This self-extinguishing arrangement (called a sniffer arrangement in the source notes) is found in the Velox lamps made by J.K. Dey in India. The wick tube is surrounded by an outer tube, so when the oil vessel is opened downward, the flame goes out by itself.
Q17. Have you heard of the Velox GL-50 and GL-60 safety lamps?
Answer: Yes, GL-50 and GL-60 are two types of safety lamp made by J.K. Dey and Sons of Kolkata. Both are approved by DGMS for degree I, II and III gassy mines. The difference is that the GL-50 has no internal relighter, while the GL-60 has one. Both are top-feed lamps, and the GL-60 also has an under-feed arrangement.
Assembly and Everyday Handling
Q18. In what order are the parts of a safety lamp assembled?
Answer: Inside the bonnet go the large gauze, then the small gauze inside it. Next comes an asbestos packing ring, then the large glass, then a second asbestos packing ring, and last the glass retainer ring, which is screwed onto the threads and tightened with its key. The top assembly is then ready. It is placed on the oil vessel and turned until the threads are fully tight.
This assumes that filling the oil vessel, checking or changing the battery, checking the filament and trimming the wick have already been done. For the relighter, see Figure 4 below.
Q19. What is the work of the glass of the lamp?
Answer: The glass does two jobs: it protects the flame from gusts of air and it increases the light of the lamp.
Q20. What is the highest air speed in which the lamp can burn? Why does the law forbid blowing the lamp out?
Answer: The lamp is safe up to an air speed of 15 m/s. Above that, there is a danger of the flame getting out, and the danger is greater if the gauze has already become very hot. This is why the law says that when gas flares up and burns inside the gauze, no one should try to put out the lamp by blowing on it.
Q21. What happens if a burning lamp is kept tilted?
Answer: If a burning lamp is kept tilted, the glass may crack.
Q22. What will you do if the glass of the lamp breaks in the mine?
Answer: Pull the wick down to put the lamp out and inform the sirdar or overman.
Q23. How can you tell, without opening the lamp, that the gauze is not working or is damaged?
Answer: If the bonnet feels hotter than usual to the touch, the gauze is probably broken or its holes have been blocked by soot.
Q24. Where and why are packing rings used? What are they made of?
Answer: The packing rings sit above and below the large glass. They keep hot gases and smoke from leaking out of the lamp and keep the glass tight. They are round rings made of asbestos, which is not affected by heat and does not burn.
Q25. Which fuel should be used in a safety lamp?
Answer: Either petrol or a solvent spirit such as Solvent Spirit 1425 (Esso) or an equivalent.
Q26. Can a safety lamp with a flint-wheel internal relighter be used?
Answer: No. A lamp with a flint-wheel relighter is not permitted in the mine. Such lamps were used earlier but not now.
Q27. What does it mean if the safety lamp is hotter than usual?
Answer: It means one of two things: either the gauze holes are blocked with soot because the lamp was not cleaned properly, or gas is present and is burning inside the lamp.
Types of Flame Safety Lamp
Q28. What are the types of oil safety lamp?
Answer: Oil safety lamps are classified in two ways:
| Classification | Types |
|---|---|
| By way of air entry | Top feed Top and under feed (top feed, bottom feed) Mid feed Under feed |
| By relighting facility | Relighting type (with an internal relighter) Non-relighting type |
Q29. Give an example of a top-feed and under-feed lamp.
Answer: The Velox GL-60, made by J.K. Dey and Sons, Kolkata, is a top-feed and under-feed lamp. It is approved by DGMS for degree I, II and III coal mines. Its chimney goes straight up, and it has air inlet holes below the glass, which are closed with the shut-off ring when the lamp is used as a top-feed lamp. The hot fumes leave through holes at the edge of the roof. Since it is a low lamp with a flat top, checking a thin layer of gas near the roof is easier.
Q30. Why is the small glass not fitted in safety lamps nowadays?
Answer: The small glass interferes with gas testing, so it is no longer used.
Q31. Why is only a round wick used in the safety lamp?
Answer: On a flat wick, the gas cap looks different when viewed from different directions, and the gas test can go wrong. For this reason, the law prohibits the use of a flat wick, and DGMS now approves only lamps with a round wick.
Internal Relighter, Weight and Feeds
Q32. What is an internal relighter? How does it work?
Answer: An internal relighter is an arrangement in the lamp that allows you to light a lamp that has gone out without opening it. One or two torch cells (battery cells) are fitted in the oil vessel, and a filament wire is fitted next to the wick. Turning the screw at the base of the vessel completes the electric circuit, the filament glows and lights the wick. Once the wick has caught fire, the screw is turned back to its old position.
During percentage testing the lamp sometimes goes out. To keep the lamp useful for gas testing, DGMS has accepted only lamps fitted with relighters for use by sirdars and overmen.
Q33. Why does the internal relighter sometimes give trouble?
Answer: A relighter gives trouble in these situations:
| Cause of trouble | What to do or why it happens |
|---|---|
| Fall in cell voltage | Two 1.5 V cells in series give 3 V. When this falls to about 2.3 V, the current can no longer heat the filament properly. |
| Coal dust or fuel dirt on the wick | The wick is coated and does not catch fire. |
| Wick wet with water | A wet wick will not light. |
| Too much oil on the wick | Shake the lamp gently by hand or blow at the inlet hole. |
Q34. How much does a safety lamp weigh?
Answer: The weight varies with the make, but roughly a safety lamp weighs about 1.75 kg. The Velox GL-50 weighs 1 kg 650 g with oil, and the GL-60 weighs 1 kg 800 g with oil and battery.
Q35. What is the advantage of having both top-feed and under-feed arrangements in the same lamp?
Answer: Normally the inlet holes of both the top feed and the under feed are kept open, so that the flame stays steady and the lamp gives good light. Air coming in through the under feed also gives an early warning of blackdamp. When gas has to be tested near the roof, the shut-off ring of the under feed is turned to close its holes. Air then enters only through the top-feed holes near the roof, and so a thin layer of gas can also be tested.
Quick Revision Points
- The lamp has 21 numbered parts. Five pillars protect the glass, and the oil vessel holds fuel for 12 to 14 hours.
- The lamp stays alight in air speeds up to 15 m/s. Never try to blow out a lamp that has gas burning inside the gauze.
- The magnetic lock is opened with an electromagnet in the lamp room, not locked by one.
- Only round-wick lamps are used (IS:9577-1986). Flat-wick and flint-wheel lamps are prohibited.
- A lamp that feels hotter than usual has a broken gauze, soot-blocked holes or gas burning inside.
- Fuel: petrol or Solvent Spirit 1425. Velox GL-50 has no relighter, GL-60 has one.
- Oil safety lamp is classified by air entry (top feed, top and under feed, mid feed, under feed) and by relighting arrangement.
Frequently Asked Questions
Why does the lamp have five pillars?
So that a straight rod hitting the lamp touches two pillars and cannot reach the glass.
Why is a round wick used?
A flat wick makes the gas cap look different from different angles, which can cause mistakes in gas testing. Round-wick lamps are the only type approved by DGMS now.
What fuel does a flame safety lamp use?
Petrol or a solvent spirit such as Solvent Spirit 1425, or an equivalent.
Which lamps are fit for gas testing by sirdars and overmen?
Those with an internal relighter, because the lamp can go out during percentage testing.
Can a flame safety lamp detect carbon monoxide?
No. The flame shows no change in carbon monoxide, so other instruments are needed. See Carbon Monoxide (White Damp).
Keep Learning
- Flame Safety Lamp, Part 1: Construction, Parts, Principle and Development
- Mine Gases and Firedamp: Questions and Answers for Coal Mining Students
- Carbon Monoxide (White Damp)
- Mine Gases: Stinkdamp, Nitrous Fumes, Afterdamp, Sulphur Dioxide and Hydrogen
- Mine Ventilation Formulas For GATE
- Gas testing exam posts
You can also test yourself with the gas and rescue questions in Mining Safety MCQ Part 02, or visit the Indian Minerology homepage for more notes.
If these notes helped you, share them with your study group and leave your doubts in the comments.
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