I would have said its very infrequent.. in the sense I've never heard of an incident...

Maybe if the oil is old and contaminated though...

John.

Me too, i,ve never experienced this in my lifetime.

I wouldn't say that ducon, I've not lived all of my life yet...

Have you?

I witnessed a small facility that was burned out by an air compressor in the 80's. It was from the outlet flow line being too close to some combustible material that someone stacked in the room where the compressor was housed.

Air compressor outlet temperatures can reach 700-1100 Deg. F. if they are operating near continuously and if you've ever noticed the paint at the outlet is usually burned off quickly.

The heat comes from the fact that all the heat in the 14.7 PSIA air is compressed 7-10 times and concentrates that heat into a smaller space. Add to that the mechanical inefficiencies and it is easy to see where the heat comes from.

On the same note, all the water vapor in the 14.7 PSIA air is compressed 7-10 times and the air is saturated as well as hot. Hence the amount of water seen in the air after it cools and condenses that moisture.

A 25 HP Compresser pumping 75% of the time will produce 18 gallons of water on and average Dewpoint day.

What is the average atmospheric dewpoint? I would think that it would vary drastically depending on the climate.

I really think that the fire start at the high pressure valves due to the accumulation of carbon from the lubricant oil and to the lack of maintenance

All air compressors running at 3 bar gauge or higher will have discharge temperatures high enough to cause the air/oil mix to ignite.In piston compressors this is caused by oil carry-over coating the valves and cabonising due to the higher temperatures. As the valves become more defective the compression temperature increases causing the carbonised oil to burn. The flash point of most mineral compressor oil is 120 Celsius, once this has been exceeded you have the ideal conditions for an explosion and fire. This normally occures not in the compressor but in the air receiver or pulsation chamber.

In rotary screw or vane compressors the explosive condition can be caused by low oil levels coupled to a defective minimum pressure valve, thus allowing an excessive pressure drop to occure across the separator element. The resultant high temperature and induced static charge can be sufficient to precipitate an explosion.

Guest, I don't believe you!!!

Honestly, does anyone use oil with a flash point of only 120 degrees Celcius??

That's only just over water boiling point you know!!

John.

A flash point of 120degC starts to bring the compressor into the domain of Hazardous Area Classification from the perspective of its electrical equipment. A higher flashpoint oil would appear to be highly desirable...

Flash point and self ignition are not the same thing. The flash point is the temperature that a substance will ignite with a flame or spark, an outside supply of heat to cause the ignition.

Self ignition is usually a lot higher (natural gas has a self ignition of about 1700F).

Good point. The flash point of the lubricant is of distinct interest in the case of a compressor, as there is the possibility of a spark being generated by two out-of-alignment metal parts coming into unintended contact with each other. In the case of electrical equipment attached to the machine, the risk of ingress of hot lubricant into a location where the chance of a spark being generated is rather high is also worthy of evaluation.

Substitution of today's lubricant with one having a higher flashpoint remains a simple and attractive option. Choice of lubricant will be mentioned in the manufacturer's information for the machine.

I know what the flash point is jmart, and for oil it should be well above 120 degrees C....

John.

Horace40:

I have heard of screw and rotary vane compressors catching fire, but have no first hand experience of any incident.

I do know that I have yet to see a well designed "modern" air cooled multi-stage piston compressor. Older or larger units employing water cooling are pretty good, but the air cooled ones I have so often seen are a disgrace from a cooling perspective and run excessively hot at the cylinder heads and exhaust areas with the only supplied cooling air flow coming from what are essentially only angled spokes on their drive pulleys. They will typically have some supplementary oil cooling of the cylinders, but that is mainly a side effect of the lubrication and is not sufficient. The simple addition of a separate thermostatically controlled fan, ducted over the cylinders and inter-coolers would do wonders.

what lubricating oil are you talking about? On constant discharge a compressor might run long enough for engine oil (cylinder lubricating oil) to get hot--but catch fire? Nah? The oil would tend to limit heat, lack of oil would create heat from friction...until compressor failure (e.g. seizure). So the practical answer is: practically never. The cure is: use and maintain according to instructions; and don't worry about it. If you're just blowing air (keeping engine cycled on) take a break periodically to give the engine a break...or prevent safety cut-off from giving it a break.

Hello

If the discharge temperature is over or close to flash point of lubricating oil the compressor could catch fire.

Aurel Mares

Deputy Mechanical Plant Coordinator

S. C. Petrotel-Lukoil S. A.

Phone: (+40) 727 377 185

Fax: (+40) 244 512 031

E-mail: AMares@Petrotel.LUKoil.com

Incorrect alignment and tension of the drive belts on the air blowers at a water recycling works caused a minor fire that was quickly extinguished by using the emergency stop button and a hand-held extinguisher.

Wow. In twenty five years of using air compressors in my lab at work and in my shop at home, I've never had any such thing happen. I've seen fried motors, blown valves/reeds, and snap-crackle-popping outlets and plugs. But I've never witnessed or even heard of compressor oil starting a fire.

Sounds to me like you had a surprising little event.

Most of what follows applies to rotary-screw compressors:

I worked for a screw compressor manufacturer for about 5 years and they mentioned that the last flash fire they had heard of was from the 80's. If I remember correctly, flash fires would occur when the compressor would suddenly stop with the separator tank at full pressure (generally the compressor would seize). Then the high pressure oil-air mixture would rush back into the extremely hot compression module. The sudden change in pressure would vaporize the oil and greatly reduce the flash point for this oil-air mixture and then if there was enough heat or any sparks ... POOF! The main way they combatted this problem was through adding discharge check valves so the air could no longer suddenly rush back into the compression module from the tank and also by changing the shutdown sequence. Also they have made big improvements in the control software to monitor oil and air temps in order to shut down the compressor when it is in danger.

As far as the outlet temperatures, they depend on the type of compressor with oil-free compressors being a lot hotter than oil-flooded. The majority of the horsepower you put in the compression process actually comes out as heat and the oil-flooded designs remove heat from the outlet air much better. A well designed compressor package has a cooler for the air that gets it down to outlet temperatures that won't cause things to catch fire, but I still wouldn't want to pile a bunch of newspapers or anything flammable close to the outlet or the package itself. I think 3' is the recommeded clearance.

Hope some of this helps.

To all the doubting Thomas's, compressor fires happen.

Oil-flooded compressors for shop air service run at temperatures of 180F to 220F depending on the compressor design and the ambient conditions (enclosed building, boiler room, summer, winter). The discharge pressures run the range of 80 psig to 200 psig with most units designed for between 100 and 150 psig. This results in a hot compressed air/oil mixture which only needs an excuse to ignite, sometimes explosively. The resulting damage can range from internal and self contained to total destruction of the building or factory which contains it. Most incidents are minor in nature and only happen a few times per year in the U.S. Major events are rare. That's a pretty good safety record considering all the oil-flooded units in service throughout the U.S.

The high operating temperatures are required to prevent water from condensing inside the separator tank. These conditions require oils specially designed to operate there. Some people have tried to substitute gear oil for compressor oil only to find themselves with the "opportunity" to buy a new compressor to replace the one they just "broke".

Failure modes include static charges building up in the separator elements resulting in ignition of the air/oil mixture (unusual), relief valves activating and spraying hot oil all over the electrical switch gear resulting in a fire (unusual), and self ignition (very rare). The first two failure modes require equipment failures. The static charge mode is prevented by providing an electrical ground between the separator filter element and the steel separator tank. The relief valve failure mode is prevented by making sure all the controls are working properly, the relief valve pressure setting is correct for the application and that the air/oil mixture is directed away from electrical equipment. Self ignition is prevented by making sure the control system is functioning properly, the coolers are clean and using the correct oil.

A: It happens a lot because people will simply forget to change the oil air separators,oil, and replace intercoolers when they need to. It happens on water well and oil and gas drills a lot.

Proper maintenace at normal intervalsis the only solution period.

Thanks for all the replies. Very interesting.

On balance it seems to be a likely possibility waiting to happen. Albeit not often.

I have been Googling on the subject and there are hundreds of references to compressor fires - some with horrendous consequences (the Wilberg mining disaster in 1984 killing 27 people - but only a few are specific on how it came about.

A general explanation can be found at:

http://mshawebapps.msha.gov/S&HINFO/TECHRPT/FANDE/OILROT.pdf

Reading this article, it is logical for compressor oil to catch fire when undergoing compression. The conditions for this to happen are lurking in the background waiting to pounce on the unsuspecting tardy maintenance engineer.

If it was not possible for this to happen then diesel engines would not work.

As a supplementary question (as someone with an interest in compressed air for breathing apparatus) - until such time that the compressor shut down (blew up) would the compressed air being delivered contain enough carbon monoxide and other toxic combustion products to worry about?

Apart from health and safety, would the compressor be knackered - or would it be a quick way to do a decoke job.

You most definitely do not want to use a conventional compressor for breathable air even though it is theoretically possible with the right air treatment. I assume you don't mean for scuba applications or presumably you would certainly know that already.

There are compressors that are certified for producing breathable air ... stick with one of them.

You are right Greg C. I do know (a bit) about SCUB breathing air compressors already.

I ask 'silly' questions as a technique to assess the reliability of answers I get.

If replies to my 'silly' questions are 'correct' then I can attach a high degree of confidence to the answers to my other 'sensible' questions.

My general question about compressor fires was to find out the extent of the problem.

You are right when you say you should not use conventional compressors for breathing air, but in practice that is exactly what happens. Similarly you are right when you say you should use certified compressors - and again in practice that is exactly what happens.

A problem arises here because conventional compressors and certified compressors are the same. It is only the type of oil used and the air treatment that makes the air fit to breathe.

The problem is made worse by the lack of standards for selection, use and maintenance. Thus people are hooking up to any old compressor system in the belief that the air is breathable. SCUB divers especially.

The evidence that the air is not 'breathable' will only carry weight when it can be proved that people are being killed. Until then, no one will take any notice.

Hence my original question.

Horace40:

I remember reading several times over the years that a number of people have been sickened and killed by breathing air from an unsuitable compressor (deaths in SCUBA incidents were particularly noted) but I have no statistics or references at hand.

I do know that in instances I encountered where breathable air was required for respirators in industrial settings, it was typically supplied by compressed air tanks that were specifically obtained for that purpose, and were tagged as such from the gas supplier.

SCUBA applications (besides requiring high pressure compressors to fill the tanks) are particularly sensitive due to all the factors involved in breathing air under pressure during a dive, and the fact that the effect of any contaminants can have a much greater effect.

Most fatalities resulted from the improper location of air intakes on IC engine driven compressors which resulted in some CO being mixed with the air (this can also occur from the lubricating oil in overheated piston compressors driven by any means), but incidents have occurred from all manner of contaminants that became mixed with the air including fibers or particles from the compressor, associated plumbing or hoses.

I'm just elaborating on this issue since it was raised, and can have potentially life threatening consequences.

This link furnishes some guidelines on compressed breathable air for applications other than in life support systems or SCUBA .

http://www.dot.state.ny.us/progs/safety/sb-94-5a.html

Another link with info:

http://www.ecompressedair.com/library/breathingair.shtml

Greg

Hello Greg G

Thanks for the links. I appreciate you giving thought to the matter and taking the trouble to reply.

The Del-Monox purifier in it's various forms has been around for a long time. Deltech entered the field back in the 60's and I assume they are still going strong. Their products are pretty high in price (as are most other makes of proper purifiers) and the cost puts people off.

It is so easy to save money by pretending there is no toxic contamination risk - hence my original question about the likelihood of compressor fires.

Compressors can overheat enough to burn the oil to generate large amounts of toxic combustion products - except that no one knows it is happening - whereas as fire itself is likely to attract attention.

I was hoping to get some info on actual incidents with the help of CR4 contributors.

I have worked for several companies performing service in the field for various plants for 35 years. I have seen the results of a nimber of air compressor fires, both on piston and screw compressors. On piston compressors it can be that the customer was using a motor oil ( which has a lower flash point and forms a carbon easier )rather than a compressor oil ( which typically have a flash point around 400*F ). On screw compressors a likely cause is static discharge in the separator when someone removes the staple placed on the the gasket by the gasket as an electrical path to eliminate this possibilty.

Horace40:

Many people have been killed as a result of compressor fires it turns out. The single biggest death toll I found was in 1984, the Wilberg Mine disaster which claimed the lives of 27 miners and was attributed to an improperly maintained air compressor which caught fire. That disaster is mentioned in at least 2 of the links below.

Some links related to compressor fires:

http://www.hanford.gov/rl/?page=778&parent=748

http://www.tribology.co.uk/services/investigate/explosion.htm

Scroll down to compressors:

http://www.msha.gov/REGS/FEDREG/FINAL/1996FINL/5453(2).htm

http://mshawebapps.msha.gov/S&HINFO/TECHRPT/FANDE/OILROT.pdf

Scroll down to #3:

http://hss.energy.gov/csa/analysis/oesummary/oesummary2004/oe2004-08.pdf

A compressor fire in a compressor that supplied breathable air killed the person breathing it:

http://touchngo.com/sp/html/sp-3788.htm

Scroll down to #3.0:

http://www.oiltech.com.au/bulletin/bulletin_text/firesafe.htm

http://www.chemandlube.com/TECHNICAL%20DATA/compressor.pdf

Scroll down to page #26 "Compressors":

https://www.dol.gov/msha/regs/fedreg/final/96_5453.pdf

Regards,

Greg