LEL protocols

Hi all,

I'm having a discussion with a colleage about LEL responses. The instance in particular is an enclosed testing room, which has natural gas and propane fuel lines. The space is not classified, but does have LEL sensors. The current response in the control sequences states that upon a 20% or 40% LEL alarm, the test shall be shutdown, fuel sources cut off, and ventilation indexed to 100% OA. Since the response to both alarms is identical, I'm wondering why both are needed? My premise is that potentially at 20% LEL, the test shall shutdown, fuel sources shut off, and ventilation indexed to 100% OA and max flow. Under 40% LEL, perhaps ventilation then should also be shutdown,(or some other reasonable response)as the equipment is not rated as explosionproof. It just seems odd to me that the response to both alarms should be identical given that the level of one condition is far greater than the other. I'm looking for feedback from others on what their typical responses are to these alarms. I've had extensive experience, but only in one environment, so looking outside those walls would be a good thing. Thanks in advance to any input.

Russ

I would favor a 3 step control strategy
1. at 10% warning light comes on and ventilation is increased and maybe ramped proportional to LEL
2. at 20% test could be shut down or additional ventilation that would ventilate room at one turnover per minute or so
3. After one minute delay of additional ventilation and still above 20% shut all gas sources off and shut down test.

MOST IMPORTANT than all this control stuff is - are all your ignition sources rated for this environment. Do you have proper pilot lights and ignition controls on combustion equipment?

AND why do you think you will be getting this much gas in room? Failed pipe or fitting sure but are you really thinking that under normal operations you are going to get this much gas?

Some of this I base on experience as submarine battery charge electrician and yes we did generate hydrogen of course. Second qualification is as industrial hygienist with experience working around gas emitting sources and combustible flammable confined spaces.

Dan Bentler

In a natural gas compressor station. 5 compressors, 10 LEL sensors above the compressors. At 20% LEL fans are turned on three at a time in increaamnets of 5 seconds. There are 10 fans. At 50 % LEL the compressors are shut-off and the compressor station is blown-down . All gas lines within the station. ( suction,discharge and fuel lines)

I have seen similar scenarios to what Mickey has described:

20% LEL - Exhaust fans on, alarm beacon on

40% LEL - Shutdown (ESD)

Yep I think its industry standard. 20% turns on Fans or some sort of device to vent the building, 40% ESDs and blows down the system. Anything else is cutting it a little close

Thanks for the input

Thanks to all for the responses. It sounds to me like a staged approach is correct. The response I am getting from the colleage is that if we have a 40% LEL or greater, it makes no sense to shutdown area ventilation. In his mind, the ventilation is the only thing that can bring the LEL condition back to a normal level. My only response is that in my experience, the effort to reduce the LEL is initiated at 20%(or close to), and is abandon at 40%, essentially saying that the effort to bring the LEL down was ineffective. My point also is that because the LEL is uncontrollable with ventilation, running said ventilation or any other equipment only serves to enhance the potential to provide ample energy to cause an ignition. As such, your experiences mimic that of what I have seen. I'll be more willing to not alter my position on this subject in the future. Any other input is still welcome.

Russ

My example did not turn the fans off at 50% LEL. They stayed running and piping was blown down. Turning fans off does not make any sense to me, you want to get the gas out of the building.

russrmartin said:

Thanks to all for the responses. It sounds to me like a staged approach is correct. The response I am getting from the colleage is that if we have a 40% LEL or greater, it makes no sense to shutdown area ventilation. In his mind, the ventilation is the only thing that can bring the LEL condition back to a normal level. My only response is that in my experience, the effort to reduce the LEL is initiated at 20%(or close to), and is abandon at 40%, essentially saying that the effort to bring the LEL down was ineffective. My point also is that because the LEL is uncontrollable with ventilation, running said ventilation or any other equipment only serves to enhance the potential to provide ample energy to cause an ignition. As such, your experiences mimic that of what I have seen. I'll be more willing to not alter my position on this subject in the future. Any other input is still welcome.

Russ

Click to expand...

Russ
I think turning off ventilation is a mistake. That is the LAST thing you want to do - in my mind it is not an option YOU MUST VENTILATE
examples
1. Coal mines use ventilation to keep gas levels below the LEL.
2. Drilling landfill gas extraction systems in landfill - we were getting (if recall correct)60% methane and 30% CO2. We were using 8" steel casing and welded and cut on it with the gas being emitted thru pipe. We used drill rig air compressor to keep LEL below 10% (??) - worked like a charm.
3. Submarine battery charging - if the battery well exhaust fan could not keep up with hydrogen while charging then you could shut down charge crank up diesel generator and ventilate the battery well with both the fan and the engine while charging - worked like charm.

Depending on your fan setup you will need proper rated (explosion proof) fans for whatever gas you may handle.

Dan Bentler

In this application, the space is not rated as hazardous, and none of the ventilation equipment is or will be EX. This is why I was advocating shutting down the ventilation. My experience has been with process ventilation, not general space, and in all instances the area was classified in some manner. Does the fact that the fans will be GP change your position on shutting them down? My colleage feels as you do that they should always be active to remove the flammables, if they are ever detected.

Fans have to be active. Let's not discuss equipment here, but people in the room. Ventilate, and evacuate. If you can't evacuate for whatever reason you do not want to poison the survivors with gas.

To recap the procedures:

20% alarm -People out, ventilation started, shutdown of gas in room
40% alarm - shutdown of external gas supply

There aren't any discussion options. If you have a gas detector, there are rules to follow. We maintain gas heads with a 50% bottle, and that's just barely below the shutdown alarm.

Thanks all

Got it. Really, regardless of location classification, ventilation should be run at all times. The fact that we are enacting all precautions possible at 20% LEL simply makes for a safer environment. Thanks to all again.

Russ