No abstract

One of the more important collapse modes for straight, combination, and extension ladders is base slide out; the top of the ladder slides down the support wall as the base slips away from it. Various fundamental models have been used to study this behavior. This paper revisits the analytical solutions associated with these models and describes their implications for the analysis, design, and testing of ladders.

No abstract

The electric heating pad represents one of the medical devices that escaped the FDA safety net by a “grandfather” exemption. An amazing number of philosophical safety issues are introduced by this relatively innocuous commodity. Pain relief is a major attribute of heating pads followed by a minor in actual medical efficacy associated with the improvement of local blood circulation. By contrast, the historic downside is very dramatic featuring electrocution, fire, and skin burns. This paper begins with a brief introduction to current protocol for placing new medical devices into the stream of commerce. In the case of heating pads, it is fortunate that the Underwriters Laboratories Inc. developed and promulgated design rules that effectively mitigated the dangers of shock/electrocution and fire. On the other hand, UL has not undertaken a technical program that addresses the skin burn problem that is the focus of this paper. Nevertheless, many heating pad manufacturers are under the impression that their compliance with UL 130 has ameliorated the skin burn propensity of their pads. Heating pad manufacturers have attempted to control skin burn injuries exclusively through the means of on-product and in-manual warnings that have been promulgated by UL, FDA, and CPSC. This approach has tenaciously maintained a burn rate of 1600 cases per year. A different approach to the skin burn problem is automatically orchestrated by invoking the “Safety Hierarchy.” For example, falling asleep and causing prolonged skin exposures to a heated pad can be eliminated by a dead-man control. Exposure to extreme temperatures that arise when both faces of the pad are concurrently covered is perhaps the most prevalent cause of skin burns. This paper exploits the notion of monitoring both face temperatures and shutting off the pad when they are almost the same. We also explored shutting down the pad when the cycle rate of the bang-bang controls was sufficiently slow; higher heating rates are associated with an uncovered face.