I have been looking into this topic since 2010, when it was first presented to me. The hoods that I dealt with claiming zero clearance to combustibles (or reduced clearances) were based on tests taken out of the 1995 Edition of UL 710. This edition does not cover any question regarding clearance to combustibles. We did not approve these hoods for their reduced clearances based on the documentation presented. This year, during the ICC Committee Action Hearings, a proposal was submitted to permit reduced clearances to combustibles for Type I hoods. The proposal was based on information added to the 2012 Edition of UL 710. The new information contained provisions for reduced clearances to combustibles for Type I hoods. The proposal was approved by the committee, but still has to make it through the ICC Public Comment Hearings at the end of September. If it goes through, this proposal will be included in the 2018 IMC. My jurisdiction recently adopted the 2012 ICC Codes. To consider approving a Type I hood for reduced clearances to combustibles based on UL 710 in my jurisdiction, one would have to submit a code modification request asking that the (possible/probable) language contained in a future edition of the code (two editions forward) be used as a basis of approval. That in itself is a stretch, but not impossible. The problem would be determining which hoods are tested to the 2012 Edition of UL 710 and which were tested to the 1995 edition that didn't include those provisions. If that were not possible, IMC 304.1 states "Where conflicts between this code and the conditions of listing or the manufacturer's installation instructions occur, the provisions of this code shall apply." Until my jurisdiction adopts the 2018 IMC, there is a conflict between IMC 507.9 and what the manufacturer is providing for reduced clearances to combustibles.
