Fire/Arson Investigations : Fire/Arson Investigations
A place to ask questions and add to probative and informative discussions associated with the various aspects of the field of fire investigation. -- FORUM RULES---BE CIVIL AND NO NAME CALLING, NO BELITTLING, NO BERATING, NO DENIGRATING others. Postings in violation of these rules can be removed or editted to remove the offending remarks at the discretion of the moderators and/or site administrator.
Re: New National Fire Protection Association's 921
Posted by: J L Mazerat (IP Logged)
Date: January 07, 2020 12:15PM
From what I see it is gone for the next edition.
I believe Section 23.8.1 is still misleading. It states, “Gaseous fuel-air mixtures are the most easily ignitable fuels capable of causing an explosion. Minimum ignition temperature is in the 370oC to 590oC (700oF to 1100oF) range are common, and they can be even lower for heavier hydrocarbons such as n-neptane at 215oC (419oF). Minimum ignition energies of some selected fuels are shown in Table 23.8.1. While Table 23.8.1 shows single values, minimum ignition varies with the fuel air ratio shown in Figure 23.8.1 for methane". This leaves the reader to believe that only a change in the fuel air ratio will cause a change in the minimum ignition energies. The ASTM standard that is used in the development of these values states with the fuel air ratio being the exact same the values recorded from different test can have a range of +/- 10%. I do not understand why the committee refuses to add the information from the ASTM standard for clarification.
I believe there is a contradiction between section 5.7.2.1 and 5.7.2.2. 5.7.2.1 states, "Flammable gases can only be ignited by a spark or pilot flame over specific ranges of gas concentration. These limits are normally expressed as the lower flammable/explosive limit (LFL/LEL), the lowest concentration by volume of flammable gas in air that will support flame propagation, and the upper flammable/explosive limit (UFL/UEL), the highest concentration of flammable gas in air that will support flame propagation. These limit concentrations fluctuate with temperature and pressure changes, and with changes in oxygen concentration." The key word is the word "only". This means there can be no other cause for ignition.
5.7.2.2 states that you can have an autoignition from a hot surface. This means there are more than the two reasons for ignition cited in 5.7.2.1.
There are just a couple of examples. I am not saying there is not an improvement in the document but I do see there is a reluctance in the new committee as it was in the old to address specific areas where the text is in conflict with itself or is in error.
Jim Mazerat
Forensic Investigations Group
I believe Section 23.8.1 is still misleading. It states, “Gaseous fuel-air mixtures are the most easily ignitable fuels capable of causing an explosion. Minimum ignition temperature is in the 370oC to 590oC (700oF to 1100oF) range are common, and they can be even lower for heavier hydrocarbons such as n-neptane at 215oC (419oF). Minimum ignition energies of some selected fuels are shown in Table 23.8.1. While Table 23.8.1 shows single values, minimum ignition varies with the fuel air ratio shown in Figure 23.8.1 for methane". This leaves the reader to believe that only a change in the fuel air ratio will cause a change in the minimum ignition energies. The ASTM standard that is used in the development of these values states with the fuel air ratio being the exact same the values recorded from different test can have a range of +/- 10%. I do not understand why the committee refuses to add the information from the ASTM standard for clarification.
I believe there is a contradiction between section 5.7.2.1 and 5.7.2.2. 5.7.2.1 states, "Flammable gases can only be ignited by a spark or pilot flame over specific ranges of gas concentration. These limits are normally expressed as the lower flammable/explosive limit (LFL/LEL), the lowest concentration by volume of flammable gas in air that will support flame propagation, and the upper flammable/explosive limit (UFL/UEL), the highest concentration of flammable gas in air that will support flame propagation. These limit concentrations fluctuate with temperature and pressure changes, and with changes in oxygen concentration." The key word is the word "only". This means there can be no other cause for ignition.
5.7.2.2 states that you can have an autoignition from a hot surface. This means there are more than the two reasons for ignition cited in 5.7.2.1.
There are just a couple of examples. I am not saying there is not an improvement in the document but I do see there is a reluctance in the new committee as it was in the old to address specific areas where the text is in conflict with itself or is in error.
Jim Mazerat
Forensic Investigations Group
Sorry, only registered users may post in this forum.