The term “smoke testing” is used in several different contexts. Often, people use it to refer to a test of a system such as a vacuum system or plumbing system, in which smoke is literally forced through the system to look for leaks and other problems. This term can also be used metaphorically when talking about testing other things, usually in the sense of a quick test conducted to confirm that the system being tested is operational, even if it only functions on a very basic level.
One case in which smoke testing is widely used is in testing of sewer systems. Smoke testing can be used to identify leaks as well as inlets, and may be used if sewage is spilling out, backing up, or if other problems are being experienced. In this type of smoke test, nontoxic smoke is blown through the sewer system, and observers watch for plumes of smoke which can reveal tell-tale problems. This type of testing is usually performed by public works employees for the purpose of monitoring public or environmental safety.
While the smoke used is not toxic, it is generally not a good idea to inhale it, as it can be uncomfortable. People working on the system may wear facial protection to reduce the risk of inhalation, and observers may be advised to stand back. Once the smoke clears the system, it will dissipate harmlessly.
Certain types of closed and vacuum systems can also be tested with smoke testing. In this case, the technician wants to confirm that the system is truly sealed before filling it, so it is filled with smoke and the smoke is monitored. If smoke escapes, the system is not closed, and this needs to be addressed. This type of smoke testing reduces waste and the risk of exposure to toxins by ensuring that a closed system is really and truly closed before it is filled.
People also sometimes refer to quickly plugging in electronics to confirm that they are functional as “smoke testing.” In this case, the equipment is plugged in and turned on to check for any obvious problems. This may be done during development or repair due to safety concerns or worries about how repairs are going. “Smoke testing” is also used in software development, to refer to a quick test in which the software is activated and the technician waits to see what happens. If the software fails catastrophically, it is time to return to the drawing board, and if it functions, more extensive testing can continue.