Misconception in Electrical Scope in Area Classification Assessment

[ThePunisher]

Hi all,

I was given a scope wherein Electrical has to make an assessment what are the limits wherein a mixture is said to be capable of developing flammable/explosive atmospehere. The "mixture" is in the form of a mine tailings which consist of a combination of several materials like sand, water, iso-Pentane, n-Pentane and many others. Process provided me with a table that spits out the % content, density, etc of each items in the mixture. Then it is expected for me to tell them whether the mixture composition exposed to certain temperature and pressures, will create an area classification.

They also expect Electrical to tell them at what % content and/or density of mixture (where the ios-Pentane, n-Pentane) will it result to an area classification so Process can use these information to set limits on the process accordingly.

I started to read NFPA 497. However, I am blown away with the fact the ELECTRICAL is even doing this and perhaps there is a misconception on what Electrical can possibly do in making the area classification assessment. NFPA may indicate density in air, LEL, etc of single chemicals but not on a mixture. I am not even quite sure if this is Electrical's job as I used to make area classification using results of an area classification assessment report.

I would like to obtain guidance in this forum to ensure I am not doing things that are not solely in our scope, whether there is a misconception or not, what is the right path-forward and any reading or reference I can use (including any forum subjects). Thanks!

 

[X49]

Area classifications usually fall into the EE's scope of work since they are defined in the electrical code (in US and Canada). The definitions in the code can be vague, and somewhat confusing. They rely on the engineer to make a judgement call regarding the concentrations that may be present in the air, as well as the frequency at which this will occur.

For certain applications, there are more specific standards (such as NFPA 820 for wastewater facilities), which can greatly help in determining area classifications. I'm not sure if there are any standards that fit your application.

Ventilation is also a factor that can affect area classifications.

Ultimately, the area classification should not be determined by you, and you alone, but should be coordinated between the Process/Chemical, Electrical, and HVAC designers. I have personally been involved in an incident where an explosion occurred, partly due to a lack of coordination between Electrical and HVAC designers.

 

[Compositepro]

Electrical will determine area classification based on potential LEL's provided to them. It is not reasonable to expect an EE to determine potential LEL's of different mixtures of chemicals. The calculations can be very complicated even for ChemE's to understand. Plant process engineers who understand the manufacturing process and possible failures and upsets would have a lot of input. Often these decisions are made very conservatively with CYA being a big factor.