All about Lower Explosive Limit (LEL) and Upper Explosive Limit (UEL)

grim

Most commercial gas detector control units are not explosion proof, however, they are intended to be installed in unclassified locations, and wired to remote sensors that are classified. Which highlights a fundamental truth about explosion proof and classified locations. The best approach is eliminate everything but non-essentials, remove circuits if necessary, and locate as much as possible outside of the classified area.

Kapea

And hope your transmitters don't malfunction.

Detectors are there to warn you, BEFORE an explosion occurs. Who cares what they look like afterwards?

TheMechWarrior

Ethanol vapour is a funny beast, we did some explosivity tests cover the full range and if the ethanol vapour strength was too high you get nothing, if it's too low you get nothing.

There's a sweet spot of ethanol to air at which point if you supply an ignition source you'll be in trouble. That sweet spot is quite a narrow bandwidth!

I'll see if I can find the report.

punkin

Tween 3.3% and 19% apparently. Flash point 365C

Lower and Upper Explosive Limits for Flammable Gases and Vapors (LEL/UEL) Reference Information (PDF)

Unsensibel

@Kapea said: And hope your transmitters don't malfunction.

Detectors are there to warn you, BEFORE an explosion occurs. Who cares what they look like afterwards?

It's not how they look before or after but how they behave. What @grim means with classified/ex/intrisically safe is that if there's a mixture between LEL and UEL, the device doesn't provide an ignition source.

grim

@Kapea - Yeah, which is why I made the point earlier about the best approach to EP/Ex/Classified is to remove or move anything and everything possible. Not only is it cheaper, but it's safer since even EP isn't considered 100% failsafe. Probably find that it's the cheapest solution as well, since it's a whole lot easier to tear out circuits than to have an electrician run sealed conduits for an EP outlet you'd never use. The irony is that explosion proof doesn't mean it's explosion proof, only that if a failure inside of the device created an explosion in the device, it would be contained in the device and not turn it into a grenade. Doesn't at all mean it can't or won't fail and cause an explosion.

The other approach we're using is to have every outlet, conduit, circuit, panel, switch, etc in the building at least 5 feet off the floor. No radios on the floor, power strips, computers, etc. The reason 5 feet off the deck is to treat all of the floor as a potential spill area. This is greater than the NEC recommendation (depending on your interpretation).

Also, have absolutely no essential electrics a 5 foot radius from the edge of the still, processing, storage area, etc. If there is a light within 5 feet of the top of the still, get rid of it. Control panel only 3 feet away from the edge? Move it. solenoids/actuated valves? Move them.

Essentials for us? Agitator and temperature sensors.

For the RTDs on the still - we separated them from the controller using Intrinsic Barriers (aka Isolating Barriers). They'll protect from the RTD failing or being passed any appreciable current in a failure situation. These are pretty easy to use, they just wire in-line with the temperature probes and snap into din rail. They are passive devices, so relatively easy to use.

MTL7700 Series DIN-rail mounting safety barriers technical datasheet (PDF)

The agitator, Larry and Lloyd were able to configure us with a Class 1 Div 1 / EX motor. This will be wired up as Class 1 Div 1 with sealed conduits, explosion proof flex couplings, etc. The price of explosion proof flex coupling is outrageous.

CothermanDistilling

@TheMechWarrior - were you able to smell the atmosphere of the explosivity tests somehow? along that line, I always wonder how more nail salons don't explode...

CothermanDistilling

Agree with all @grim says...

my situation - I am only going 3' off the floor, and have one outlet I cannot really remove at 20' distance, so placed childproof plug covers in the holes until I remove the outlet and place a cover on it.... I put a 25' cord on my 'ignition-proof' pump... and I need to rectify the motorized proportional valve that is currently only 4' away.. and move/rotate one fluorescent fixture that is 5' away, but too close for comfort..

Also, the class and division have time parameters, that is how often you expect to have the flammable condition present.. I remember the non-hazardous having a 10-minutes a year time, but cannot find it now...... maybe in fire code , this is from Wiki:

Equipment Protection Level:

Zone 0 explosive atmosphere > 1000 hrs/yr

Zone 1 explosive atmosphere between 10 and 1000 hrs/yr

Zone 2 explosive atmosphere between 1 and 10 hrs/yr

ANSI/NFPA areas description:

zone 0 and 1 are: Class I, Div. 1 - Where ignitable concentrations of flammable gases, vapors or liquids are present continuously or frequently within the atmosphere under normal operation conditions.

Zone 2 is Class I, Div. 2 - Where ignitable concentrations of flammable gases, vapors, or liquids are present within the atmosphere under abnormal operating conditions.

grim

I think our goal is for the still area itself to be, at worst, a C1D2/Zone 2 area.

Even that is a nail biter, and probably not realistic without equipment failure.

My discussions with the town have been around this very point. The classification doesn't apply to non-ignitable concentrations. While small amounts of vapor will be produced in the collection process, as long as the equipment is not producing vapor, it highly unlikely that ignitable concentrations would be produced in the area.

That said, I don't think this argument is in any way a 'pass' to do whatever you'd like.

Two days ago a house in NJ exploded when workers likely disturbed a gas line, causing it to break off inside of the house (or near the entrance to the house), while repairing a main. I would guarantee the explosion was triggered by an electrical item, likely a relay, and most likely in the thermostat on the wall, calling for heat.

https://www.youtube.com/watch?v=9LuGUBPl5z8

There was nothing left of the house, all the way down to the foundation. This is what we want to avoid.

CothermanDistilling

natural gas is a dangerous mofo because of how it occupies a space, and the city lines are not dinky little 1/4psi ones like what you have after your meter... was anyone in that house, or did.... let me google......

A crack discovered in a two-inch, steel-protected gas main, 36 inches beneath Oak Avenue is to blame for an explosion that obliterated a house and damaged about a dozen others in the Cedar Run neighborhood, according to authorities.

The subsequent leaking gas jetted through a small underground water main into the basement of the house at 59 Oak Ave., where the gas ignited from a pilot light on one the utilities, said spokesman Al Della Fave of the Ocean County Prosecutor's Office.

HUH??? gas entered, went through a 60psi water main and exited, but the basement was ntto full of water? NO.... me thinks the gas followed the same hole/tunnel as the water main...

Dean Barnett, 47, a New Jersey Natural Gas employee who is also a Stafford resident, remained in critical condition Wednesday at AtlantiCare Regional Medical Center in Atlantic County. Barnett was part of a crew that was dispatched to the neighborhood on Tuesday morning to investigate an odor associated with leaking gas.

again, human detectable odor way, way, way before an explosion... I wonder what previous/current/future policies are before working on a gas main leak are with respect to the grid power for the area...

CothermanDistilling

whattya think about this for above(kinda) the still? $1500 (full retail), but LED and there aren't many other options lower priced...

Hazardous Location Fixture, T8-LED, 112W @ Grainger

similar street price is $819:
Hazardous Area LED Light -Class 1 Div 2 Groups A, B, C, D and Class 2 Div 2 F,G - 4' 4 lamp @ Larson Electronics

CothermanDistilling

heck, this has more lumens(10,500) and is cheaper($704) , yet still covers us, Class I Div 2 Group D

84 Watt Class 1 Division 2 LED Light for Corrosion Resistant Requirements - Hazardous Location Light @ Larson Electronics

punkin

Can't you have directed lights from outside the distance you need the xp?

CothermanDistilling

prolly... I guess i could get 3 or so so I don't have shadows...

punkin

Seems it's be a lot simpler and much cheaper

grim

I wouldn't put anything directly above the still, even class I div 1. How tall are your ceilings?

FloridaCracker

So, I'm guessing that the $29 ones that I have in my garage won't pass inspection......

Shit, half of them are burned out anyway.

Just following CD's journey really points out just how FRIGGING ridiculously expensive everything is when you go pro. Hat's off brother.

CothermanDistilling

@grim said: I wouldn't put anything directly above the still, even class I div 1. How tall are your ceilings?

not directly above, but within 5' likely.

9' to bottom of mezzanine truss, 10.5ft to underside of concrete/steel mezzanine. Someday hole cut in mezzanine and 16 plater happens... just not yet...

grim

I got a line on vapor detectors, self contained explosion proof enclosure. Very nice, they were pulled out of a industrial setting but you would swear they are brand new. Very affordable. Surplus guy sent me one to check, he's got a few more. They need to be class 1 div 1 hardwired with threaded conduit and seals. Has 2 relay outputs (warning/alarm), along with 4-20ma and serial output, and a nice display.

They are so cheap I'm going to pick up a second one. Using one for the general DSP floor, and a second located near the still.

CothermanDistilling

If they are preset to work with ethanol, or can 100% be calibrated to ethanol, I may be interested in 2

(I sent some to Scott/Tyco be calibrated that I bought, looked like brand new inside the XP housing, and the company refused to calibrate, I would have to buy $1000 of parts each to bring them to their spec), of course they offered new ones to me at a 5% discount...

if you want a simple panel that will work with 2-3 of those 4-20mA units, ebay search enmet cp-60, I have one i bought NIB, the rep said I could send it to factory and have it changed from 02 to ethanol for next to nothing, and enable the 3rd channel for free...

*edit - there is a 3-channel one on ebay now for $99 item number 181682950909 ... and this unit supplies the power for the sensors too, so almost a no-brainer..

grim

O2 requires entirely different sensors, it's a problem to try to convert o2 to ethanol, most cases the meter unit is designed for a single sensor type. You need to start with a unit with a catalytic LEL sensor.

Most units aren't being directly calibrated with ethanol vapor, but with a reference gas and a correction factor:

Catalytic Combustible Gas Sensors (PDF)

CothermanDistilling

sorry.. did nto mean to confuse... the head unit is only 4-20ma, it does nto know if that 4-20 is coming from a 02 or a CO or a HC sensor... it is programmed for %LEL vs 4-20mA

yes, cal kit with gas was like $500

*edit - the ones I tried to use were IR, not catalytic bead, but still used the same calibration gas...

jbierling

I have getting vapors on my todo list. I'd like the extra piece of mind.

grim

I see what you mean about the enmet, they are hard-coded internally with the gas type, it's not adjustable from the control menu. What a silly product.

The units I'm talking about are the Drager/Draeger Polytron 2 XP - they are all-in-one units that include the sensor, the controller, the display, the output control relays, and the alternative outputs (process, serial).

You can connect them to a remote panel for display, or data logging, but you don't need to. Technically everything you need to sound an alarm or trigger an equipment shutdown is in the single unit. They have two alarm outputs, so you can warn and alarm if necessary, at whatever LEL % you like (NC and NO variations).

Some snaps of the unit, next to a Killark switch plate cover for size reference.

CothermanDistilling

If you can get one to calibrate and work, I may be interested in two or three, the CP-60 is nice in that it is the 24vac power supply, and can centralize the sensors like we are looking at into a central location, which is good for me with a mezzanine and a future barrel room..

Here are the ones I had a bad experience with, they were IR, and had an incandescent IR transmitter/receiver and a mirror, and they wanted the whole 'sensor' assembly to be replaced for them to send them back to me...

Mickiboi

The Drager Polygon are the ones I am used to using. Excellent product.

grim

Man what a nice unit, works like a charm. I can't test calibration since I don't have a gas setup, but it's very sensitive. Poured a little vodka on a paper towel and put it a few inches below the sensor, picked it up right away. Waved my hand over it a few times and the LEL % reading began to move upwards rapidly. Moved it away, dropped right off.

TheMechWarrior

We use the Drager units at work. Congratulations.

grim

The guy's got 5 more, $180 each plus shipping.

Mickiboi

@grim said: The guy's got 5 more, $180 each plus shipping.

That's very very cheap.