Covering the Drain

These video captures show Steve Barnes trapping off on a compliant 12-by-12-inch drain cover to study body entrapment. By pushing himself down, Barnes was able to apply 95.8 lbs. of downward force onto the grate. He was able to release with 5.6 lbs of force. Tests such as this have confirmed that skin behaves similarly to the body-blocking element; it is slightly more likely to adhere to the cover and also easier to remove. Some standard writers hope to find a closer match to human skin.

Writers of the drain-cover standard have recently begun to perform more in-lab testing to study the dynamics of body entrapment. Here, committee member Steve Barnes “traps off” on a drain cover at NSF International labs to compare the behavior of humans and blocking elements under the same conditions.

The drain-cover recall occurred partly because of confusion in the standard’s language and mixed messages test labs received at a key meeting. For example, the body-block tests were to be conducted using an 18-by-23-inch element. Instead, testers applied an element that was close to the size of the drain. This 8-inch outlet is shown with an element measuring 9-by-11.5 inches.

A manufacturer’s product-development test pictured above, is similar in principle to the drain-cover standard’s protocol. (Photographed from the top of the tank. Fitting is installed on the wall.) Testing for certification is more strict — outlet fittings must be installed on a larger section of wall or floor, and special equipment is used to suspend the wig and measure the force required to remove it.

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