1st pic: Water leak testing in progress with a welder on top of hood doing the repairs. 2nd pic: Heavy buildup of grease from leaking ductwork above a hood is a huge fire and health danger. 3rd pic: View of electrical for hood lights from on top of hood- they are open on top of hood and grease can enter here. 4th picture- what someone tried to seal up a new grease duct with. 5th picture- inside the new duct that someone just used JB weld on a week ago!
I know many of you are frustrated about leaking ducts. With the fire in Boston showing everyone the dangers of ductwork leaking beyond where the suppression system can fight the fire, this has become very important. High pressure water leak testing has been getting done for the University of MN for many years and has worked out very well with no grease leaks in any of the tested systems. A high pressure water leak test program has now been started on new ductwork installations for several large chains. This is a low cost method that insures the ducts do not leak and also allows the cleaning contractor to verify proper access plate and fan installations. A spin jet is pulled through the entire system from the hood to the outlet at about 1500-2500 psi at 4GPM. There is a welder on site during the test with a torch to dry off the leaking point and a welder to repair the leaks. With over 200 leak tests in the past 2 years, here is what we have run in to. Approximately 10 stores passed the leak test first time with no leaks at any of the welds or in the system. All the other stores failed the initial leak test. 30 of the stores had more than 20 leaks and took at least 2 days or more to finally get them welded up so they did not leak. 4 stores had to replace all or part of the new system as the welding was so poor they could not be repaired enough to pass the leak test. Over 100 stores had 5 leaks or more and required more than one retest. 3 stores across the country had contractors who even tried to use JB weld to repair the leaks. 1 store used roofing compound. (They all failed or course and I included pictures of one from just a week ago) To keep things in prospective, almost all of these system had passed a light test, a pressure test or both before the water leak tests. Most of the major leaking found has been at the corners and at the duct to hood connections. We have had complaints about the leak testing from contractor who have been failing that the high pressure has been blowing out the welding. That is such a poor excuse. There is no way this low of pressure that is similar to what car washes use would harm a weld in any way and we have certified welders who could not believe a welder would even suggest this. One thing we have found is that once the ducts have passed the water leak test, they have not had any leakage in the future. We have a standard testing form and procedure guide available to anyone who would like them. This is the way of the future and a sure, fairly inexpensive way to make sure grease duct conform to NFPA96 and do not leak!!