Product Certification and the Real World
The business of product testing also requires that test methods be reproducible. For example, myriad factors other than the woodstove itself affect the extent to which temperatures on surrounding walls will increase when the stove is used at a specified distance. The type of fuel, the type of chimney, the insulation in the room, not to mention the finer points of product testing (for example, type and placement of thermocouples), are all significant. A test method must control these influences sufficiently to ensure that the same test will yield similar results over time. Unfortunately, the more "controlled" the test, the less likely it is to bear a relationship to reality.
This is a recurring problem in product testing. The more inexpensive and reproducible the test, the more tenuous its relationship to what happens to the product in the real world. Performance standards require that numerous assumptions be made about how the product will be used in the real world. These assumptions can take many forms. Different sections of UL 1482 appear to be based on different notions of the relationship between test methods and reality. In some sections, UL takes its lead from the NFPA standards for chimneys and venting. The stove is tested, in other words, on the assumption that it will be installed in the method recommended by the NFPA. This assumption is on the utopian side of optimistic. An NBS engineer recounts that when the Bureau contracted to have a regulation NFPA 211 masonry chimney built for testing purposes, the mason exclaimed that the chimney was unusually sturdy. "We never build them like this," he told the engineer.
A particularly difficult question for UL is to what extent it should "test for" consumer misuse. Or, as a UL engineer puts it, "How forgiving should products be?" The answer implicit in UL 1482 is mixed. Several of the tests for structural integrity in 1482 simulate what might be considered average mishaps (for example, bumping the stove door or chimney connector). Other portions come much closer to simulating "worst case" conditions. The flash fire test, for example, is supposed to simulate the kind of overfiring that would occur if, say, a Christmas tree
or cardboard box were burned in the stove. The fire used in this test burns unusually hot and much longer than in a typical overfiring situation. Chimney height affects, among other things, the tendency of the stove to emit sparks into the room. The chimney used in all fire tests simulates a kind of worst condition. According to an NBS engineer, the chimney specified by UL has an unusual propensity to emit sparks. (This is not necessarily why UL chose the chimney, however, and neither is this particular chimney required if the manufacturer specifies otherwise.)
The portions of UL 1482 that are most controversial are those in which real-world experience diverges most from testing conditions. UL generally assumes that consumers are literate, obedient, and only occasionally clumsy. Most of the test methods in UL 1482 presume that the user will follow the manufacturer's instructions. Therefore, if the manufacturer's instructions say that a grate should not be placed inside the stove, UL tests without a grate. Since the use of grates is widespread and results in higher burning temperatures, an engineer with the International Conference of Building Officials thinks that "if a conventional grate [can] be placed in a heater, then it should be tested with one." UL disagrees.
This difference in testing philosophy explains why Consumer's Union (CU), publisher of Consumer Reports, graded down a stove that UL considered acceptable. CU considered the stove dangerous because of its tendency to emit sparks through the air inlets. UL, which tests stoves in accordance with NFPA's installation instructions—including, among other things, use of a floor protector—does not recognize the problem as a legitimate testing concern. That stove poses no danger—assuming it is used with a floor protector.