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Re: Minimum Ignition Energy (mJ) of gases
Posted by: J L Mazerat (IP Logged)
Date: December 31, 2017 08:19PM
I agree 1.5 is a general warning as to the reported measurement within the document. Yes, this section can be used if the person makes an inaccurate determination and conclusion. Yes, everyone should read and understand the administration section before using the document. This is a good general warning. I look at 921 as a teaching document. Yes, you can tell the reader to go look somewhere else for information. This is a must due to all the measurements contained in the document.
Where the document is talking about mJ’s in the minimum ignition energy section in Table 23.8.1, would it do any harm to add information from the ASTM standard under the table so that when the person is reading the table the information from ASTM as to the potential variations is readily available at the same location. Adding this couple of lines of text would give the reader the precise information as to the +/- potential. More important you would be teaching the reader that it is possible that a 0.1% variation in fuel concentration could change the ignition energies by factor of 100 to 1000. This is just an idea. It may prevent one person from reading the information and wrongly presenting it to a court. What if the other side does not have a knowledgeable expert in this area. Is it worth having a person go to jail just because someone does not feel additional text needs to be added.
You may say this is redundant and that it is covered in section 1.5. To some extent it is. Then I think one needs to look at how this table is presented. The title of the Table is Minimum Ignition Energies of Selected Fuels. Throughout the document when ignition temperatures are given it is done with a range of temperatures. In Chapter 10, were it talks about ignition sources in fuel gas systems it uses a range of temperatures and stated minimum ignition energies can be as low as 0.2 mJ’s. Again, not a precise value. Yet, the table seems to be giving precise values. A could lines of text would elevate the potential for a confusion. I plan to make the recommendation to the committee. If they choose to say it is not needed so be it.
Jim Mazerat
Forensic Investigations Group
Where the document is talking about mJ’s in the minimum ignition energy section in Table 23.8.1, would it do any harm to add information from the ASTM standard under the table so that when the person is reading the table the information from ASTM as to the potential variations is readily available at the same location. Adding this couple of lines of text would give the reader the precise information as to the +/- potential. More important you would be teaching the reader that it is possible that a 0.1% variation in fuel concentration could change the ignition energies by factor of 100 to 1000. This is just an idea. It may prevent one person from reading the information and wrongly presenting it to a court. What if the other side does not have a knowledgeable expert in this area. Is it worth having a person go to jail just because someone does not feel additional text needs to be added.
You may say this is redundant and that it is covered in section 1.5. To some extent it is. Then I think one needs to look at how this table is presented. The title of the Table is Minimum Ignition Energies of Selected Fuels. Throughout the document when ignition temperatures are given it is done with a range of temperatures. In Chapter 10, were it talks about ignition sources in fuel gas systems it uses a range of temperatures and stated minimum ignition energies can be as low as 0.2 mJ’s. Again, not a precise value. Yet, the table seems to be giving precise values. A could lines of text would elevate the potential for a confusion. I plan to make the recommendation to the committee. If they choose to say it is not needed so be it.
Jim Mazerat
Forensic Investigations Group
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