Flammability and toxicity

[Sparketta]

Recently, some of my work areas have been classified as Class 1 Div 2, and I am just trying to understand all of the rules of it. The flammable liquid in house is monomethylhydrazine (MMH). The fixed structures/wiring in the area are compliant, but now we are told we cannot use our battery operated or portable plug-in meters, tools and test equipment in the area. Many people are struggling with the classification because if MMH vapors existed in concentrations high enough to be flammable, everyone in that atmosphere would be dead anyway, as MMH is IDLH at only 20 ppm, while the LEL is 2.5%. The maximum allowable concentration in the breathing zone is one part per billion. Is there no accounting for toxicity in the classifications?

 

[rbalex]

... Is there no accounting for toxicity in the classifications?

Not with regard to electrical area classification. Of course that doesn?t mean it isn?t a legitimate concern; simply that the purpose of electrical area classification is to choose equipment for the electrical installation.

I am NOT a toxicity expert. I did check a typical MSDS sheet for monomethylhydrazine. It is definitely nasty stuff. It is highly toxic but if ??everyone in that atmosphere would be dead anyway?? then one must ask what other safety measures are in place for worker safety.

The flammability range is very broad ? from 2.5 to 97%. The significance is that, depending on the leakage mechanism, while the area would indeed be toxic it could also rapidly enter the flammability range such that portable items could still ignite the area.

Technically, with the exception of certain equipment like portable lights connected to the permanent wiring, the NEC doesn?t address portable electronic devices since they are not part of the ?installation.? See the FPN to the definition of Electrical and Electronic Equipment in Section 500.2

 

[Sparketta]

Thanks so much for the reply, this is interesting stuff.

The flammability range is very broad ? from 2.5 to 97%. The significance is that, depending on the leakage mechanism, while the area would indeed be toxic it could also rapidly enter the flammability range such that portable items could still ignite the area.

This is true, and I am not arguing this point, but consider this as well: Hydrazine fuels will react with carbon dioxide and oxygen in the air. MMH may ignite spontaneously when exposed to materials with large surface areas or when it comes in contact with metal oxides such as rust. So if it needs nothing but rust or air to ignite it, our equipment sparking isn't going to make much of a difference. Since the lower flammable limit of 2.5% concentration of MMH equals 25,000 parts per million and MMH is IDLH at only 20 ppm, it would be a bad, bad day if MMH existed in concentrations that were flammable in our facility.

I realize that portable equipment is not really covered by the NEC, but OSHA does state in one of their Standard Interpretation letters that these items shall not be used in Classified areas unless approved for that area.

Yes, MMH is a nasty commodity, and we do have many controls in place. It is in a system contained in a "vehicle" with many redundant valves, etc. to contain it and is only present in our area when that vehicle is being processed. Flammable concentrations should not exist in our area unless there is a catastrophic failure, except during certain operations that are performed only infrequently involving self contained atmospheric pressure ensembles for workers- a full rubber suit with its own air supply. Before these operations the area is walked down by the fire marshall and several safety representatives and engineers to ensure that it is safe for hazardous operations. In all actuality, even during these operations there would have to be a major failure before MMH would be present in ignitable concentrations, but some vapors are expected. Toxic vapor checks are performed throughout the task. Our processes/equipment have not changed for the last 25 years or so, but all of a sudden we find ourselves working in a classified area. We are not sure why we are now classified and how everything works, hence my question.

Here is another one for you, If our "vehicle" containing the flammable liquid is no longer present, then do the rules of the classification apply? We have been told that they do not, but reading this forum I am not so sure.

Thanks for the info!

 

[rbalex]

You have added two additional points to the mix. One, the material is potentially pyrophoric, and two, “… [f]lammable concentrations should not exist in our area unless there is a catastrophic failure…”

Strange as it may seem, either could potentially indicate the area does NOT need to be classified at all. See Section 500.5(A) with regard to pyrophoric materials and API RP500 Section 1.2.1b and/or NFPA 497 Section 1.1.4 with regard to catastrophic failures.

Personally, this would take me several weeks of investigation before I would seal an electrical area classification document for the location as you have described it – and I’ve been doing electrical area classifications (both NFPA and IEC) nearly 40 years.

 

[Sparketta]

Thank you so much, Bob. I am going to check the references you listed. I agree that it is an extremely complex situation and I fear it was over classified, as it does not seem to provide any safety benefit in this case, but it is going to take some research.

I seriously doubt they had someone as knowledgable as you involved in classifying the area.