AFCI’s – Cost/Benefit

Mike, here is the substantiation for my proposal to delete 210.12. I have also attached the spreadsheet with the calculations I used to get my numbers.

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". 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 show 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 by the total number of existing housing units 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.

Note: This number is 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 21 years old. This 85% electrical fires occurring in dwelling units over 21 years old data is from the 1987 Consumer Products Safety Commission report titled, "Residential Electrical Distribution Systems Fires". This data was cited in comment 2-63 in the 1998 ROC.

This brings up the additional question of whether the AFCI breaker will still be functional, when it its needed, over 10 years after its installation. The NEMA Study ( seems to indicate that many will not be functioning at that time.

If we assume an installed cost of only $75 per new dwelling unit, that means that we would be spending $123,067,500.00 per year to install AFCIs in each of the 1.6 million new dwellings. The $75 assumes an average cost of $40 per AFCI, an average of 1.5 AFCIs required per dwelling unit, and $15 for additional labor and material that may be required such as two runs of 12-2 in place of a single run of 12-3.

If we adjust the number of fires that will be prevented by the use of AFCIs for the 15% of electrical fires that occur in dwelling units 10 years or less in age, we find that in the first year of compliance we would expect to prevent 14 fires. The cost of preventing these fires this first year would be over 8.7 million dollars per fire!

Each successive year of full compliance will result in additional fires prevented in the dwelling units that are constructed each year as well as those prevented by the previous year(s) AFCI installations. Even we these additional prevented fires are factored in we still don't have a reasonable cost benefit. At the end of 10 years, the cumulative AFCI installation cost will be over 1.2 billion dollars and the total number of fires prevented will be less than 750. The cost per fire prevented over the 10 years is still over 1.66 million dollars! Is this a reasonable cost/benefit??

If you have any questions or comments send me an e-mail.

Don Ganiere,

Mike Holt’s Comment: If you want to challenge Don’s figures, send me your figures and I’ll be glad to publish them.

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