Reading an FM Approval on ELD Equipment
FM Approvals is the testing arm of a property insurer. When equipment carries their approval, it was evaluated against a specific standard, in a specific product category, for a specific purpose. That means something, and we treat it that way.
It also means only what it says.
Leak detection equipment is certified under FM Standard 7745, and listings are issued by category. A listing for manual scanning equipment covers manual scanning equipment. Other methods were not evaluated and found wanting. They were not in that category.
High-voltage sweep is not a scanning platform, so it does not appear on that list. That is a filing distinction, not a performance one.
The real question is what your roof needs, not what your equipment is listed under
Low-voltage testing follows water. Current travels through a breach to the deck below and pinpoints it. On a membrane whose defects are open holes, it works, and it works well.
But it can only find what water can already get through.
Seamless systems fail differently. Polyurea skins in seconds and cures in minutes. Vapor rising out of a green slab has nowhere to go but up through the film, and it takes the film with it. Some of those voids stay closed and stay invisible. Others blow out so violently that bare concrete is exposed with no digging required. Both are failures. Only one of them is a hole yet, and the closed one is still going to leak in eighteen months.
Low voltage finds a void when it has already opened. High voltage finds it while it is still thin.
On a recent 11,500 square foot polyurea deck, 39 of the 42 defects we located were gas evacuations. On a roof that looked finished.
How we test
Method follows the membrane. There is no single protocol we run on everything, because the right test depends on how that system actually fails. On seamless assemblies, that is high-voltage sweep. It is the only method that finds a void before it becomes a hole.
Where a specification calls for something else, we run the correct method first and the specified method after it. You get compliance and you get the truth, and you can see the difference between them in the report.
We publish the applied voltage, how much of the deck we actually reached, and which method produced each finding. If a testing report does not tell you those three things, you do not know what was tested.