The NEC does not require the use of "combination type" AFCIs. The code only requires "branch circuit" protection. Also the AFCI manufacturers tell us that a "glowing connection" or high resistance connection is not an arc of any type and the AFCI circuit itself won't respond to these types of faults. The GFP part of the AFCI breaker will respond to these types of faults after they become a ground fault. So will a GFCI. It is my opinion that this type of heating is the cause of most dwelling unit fires.
I still find it very strange that the AFCI requirement was put into code without any statements saying how many fires these devices would be expected to prevent. Where is the cost benefit study? We will never have the technology to make our electrical systems safe and even if it was physically possible to make them 100% safe, it would not be economically possible.
I have worked up some fire data numbers using information from "Fire in the United States, 12th Edition".
http://www.usfa.fema.gov/downloads/pdf/publications/fius12th.pdf This is 1998 data. The numbers in this report are based on NFIRS (national fire incident reporting system) data. The NFIRS data accounts for 39% of all fires that occur in the US. I have adjusted the numbers by this factor to account for all fires. This data shows that there were 401,695 residential unit fires in the US in 1998. The point of origin for 12.9% of these fires was the sleeping room. Of the fires that originated in the sleeping room, 19.9% were reported to have been caused by the electrical distribution system and 11.6% by appliances. Applying these percentages to the total number of residential unit fires shows that 51,819 fires originated in the sleeping room. Of these 51,819 fires, 31.5% were caused by the electrical distribution system or appliances. This would mean that 16,323 dwelling unit fires may have been electrical in origin.
Mr. Robert Clarey of Cutler-Hammer made the statement that AFCIs could be expected to prevent 40% of these fires. This statement was made in comment 2-68 in the '98 ROC. This means that if every dwelling unit bedroom branch circuit in both new and existing dwelling units had AFCI protection, we would prevent 6529 fires per year. We now have to look at the total number of dwelling units existing in the US and the number that are added each year. US Census data shows that there were 115,253,000 housing units in 1999. 1,640,900 new housing units were built in 2000. If you divide the 6529 dwelling unit fires that would be prevented if all dwelling units had AFCIs and then multiply that result by the number of new housing units being built, we can expect that 93 dwelling unit fires would be prevented the first year of full compliance with the AFCI rule. This number is likely somewhat high as fires do not occur nearly as often in new buildings. The fire data used to get the AFCIs into the code showed that 85% of the electrical fires originated in dwelling units over 10 years old. (This brings up the question of whether the AFCI breaker will still be functional, when it its needed, over 10 years after its installation. The GFCI data and new GFCI standard seems to indicate that they won't be function at that time)
If we assume an installed cost of only $50 per new dwelling unit, that means that we would be spending $82,045,000 to prevent 93 fires. That would allow for a loss of over $820,000 per fire. Yes, I know that in some cases these fires result in a loss of life and that we can't put a dollar value on that, but corporate America does just that every day. Does the AFCI requirement meet any reasonable cost benefit analysis?
Don
