1. #1
    MembersZone Subscriber

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    Dec 2003

    Default 10% LEL Questions

    We had good size spill at the University of Minnesota last week. I am a Haz Tech and Disposal Spec. The Minneapolis Fire Dept showed first and entered the chemical storage area (not designed specifically for chemicals) where a Flammable Storage cabinet's shelves fell while a researcher was placing chemicals in the cabinet. About 24 liters was the spill size. Liquid on the floor, and the bottom of the cabinet was full of liquid. The fire dept didn't get any LEL and only about 200 ppm on the VOC (PID). So the incident was handed to the University HazMat staff. I was on the entry team and when we opened the door we got a 33 LEL, with correction factor it was about 60 something. The spill was 5 feet from the door. We got about 2200 ppm on the RAE VOC. We cleaned the spill of Hexane, Acetonitrile, and Chloroform. I know we were way above IDLH for Chloroform at the least. In the after action we discussed the fact that even if we hit 10% LEL anywhere we should back out.

    My thought is no matter what you do if you are picking up free liquid and its flammable you will hit the 10% LEL no matter what.

    Finally my questions. At what point do you back out if you hit 10% LEL? What if you are cleaning it up and hit i10% LEL?
    If you can read this, Thank a teacher. Since this is in english, Thank a Marine.

  2. #2
    Forum Member

    Join Date
    Jan 2006


    Mind you I'm only trained to the Ops level. Hopefully, I'm never put in that situation until I have the proper training and experience.

    How exactly were you guys cleaning it up?

    I did find this on the web...

    The National Fire Protection Association has assigned a flammability rating of 0 (no fire hazard) to chloroform.

    Chloroform is slightly soluble with water...so you could have put a slight damper on the vapors with some water.

    Acetonitrile is a flammable liquid. It's heavier than air, so again you could have put some water on it to control the vapors, or used the dry chem extingusher. If it did turn ignite, it produces cyanide vapors, so SCBA's would be a must.

    With the hexane putting water on it would be a waste because it would just float on top of it.

    Definitly I would be ventilating the heck out of the building.

    I realize I didn't answer your question, but I do appreciate the post. The hazmat group doesn't post enough on this board.

  3. #3
    MembersZone Subscriber

    Join Date
    Nov 1999


    I would not necessarily back out at 10% LEL-depends on a few other circumstances: Was this an initial reading after you opened the door and did the levels drop? Did you ventilate the room? If so, what were your readings after venting for 10 minutes? Did you take reading at different heights, i.e. floor, 3 feet from the floor, 6 feet up, and the ceiling? Did the readings vary or stay the same? What type of fire suppression was in place? Extinguishers? Foam? Were all sources of ignition eliminated?

    The 10% LEL warning is part of the confined space standard. 20% is the rule for non-confined space areas. Regardless if you use 10% or 20%, a good rule to follow is to back out at a pre-determined level and try to eliminate the hazard by ventilating or suppressing the vapors (foam).

    I am curious as to what type of PPE you used. Sounds like it was a real mess.
    "The most mediocre man or woman can suddenly seem dynamic, forceful, and decisive if he or she is mean enough." from "Crazy Bosses"
    Genius has its limits, but stupidity is boundless.

  4. #4
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    Join Date
    Dec 2003


    My background is Marine Corps Firefighter for 8 years so I knew what kind of boom this could have done. The fire dept shut down the supply/exhaust fans to the 7th floor and above, the supply and exhaust are on the same switch. This was an interior room with labratories all over the floor (gotta love 20 somethings doing experiments in shorts, sandles and a lab coat). The room behind this was a utility tower that runs from the sub basement to the 15th floor. The room was slightly positive pressure because of the air coming from the utility shaft. Good thing there was cardboard boxes in front of the panels to the shaft otherwise that would have been a mess.

    We used a MultiRAE for our readings. When we opened the door we got a immediate 30% LEL. With the coverstion factor the entry team leader told us to keep going because he was told it ammounted to about 6% LEL (after we got out of decon we learned it was more like 60% LEL) Later during clean-up the RAE maxed out and the LEL shut off. The readings remained the same 30 to 35% LEL though out the room. We had an ABC dry chem extinguisher with us. The room did have normal lighting, outlets, and the lights were off (no I didn't turn the lights on).

    We cleaned it up using absorbant pads, and foxtail and dust pan for the glass. Packed it into a 55 Open head steel drum and used safe step on the floor to remove the slippery feeling.

    PPE: SCBA (we were way above IDLH I believe), Syranex suit, Silver shield gloves and booties. HazMat Boots, Nitrile gloves over the silvers, and chem tape for wrists, ankles and suit zipper.
    If you can read this, Thank a teacher. Since this is in english, Thank a Marine.

  5. #5
    Forum Member

    Join Date
    Mar 2004


    How skilled is the local fire dept with air monitoring? Do they properly maintain their meters? A lot of places have problems in this area.

    You should have been in turnout gear or preferably a Thermopro(R) suit for this, since the main problem was the flammability (with SCBA). I do a lot of entry/cleanup work in turnout gear, because people tend to spill a lot of flammable solvents. Check with DuPont on how normal chemical resistant suits fare in a flash fire. They put on a good demo at both FDIC and IAFC-Hazmat. You will be convinced that you need some Nomex(R) for the job. (The Thermopro(R) has Nomex(R) in it.)

    If you have the usual 10.6 eV PID bulb, you'll only read the hexane. The other compounds have high IPs. High IPs are common on the small organics, especially if they have electron withdrawing groups on them. The halocarbon solvents have high IPs.

    Your SOPs on where you stop because of flammablity should reflect how well you maintain your equipment, and how skilled you are with the meters (including knowing about response factors). It appears that you had control of potential ignition sources, and did a good job on your monitoring, so you were in decent shape.

    The size of the spill and the size of the area are important - with free liquid you won't always get the LEL reading. You'll get a good feel for it if you do a lot of training with live chemicals. We spilled an entire bottle of toluene and only got PID hits one time, because the room was very large. Outdoors you can have puddles, and not have a LEL problem, depending on the product, the wind, and the area. At a university, you have the advantage of the lab hoods. The good ventilation forgives a lot of sins.

    You should reconsider the locations where they store that quantity of flammable materials. Flammable storage should have proper electrical classification and ventilation.

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