Systems are often used by people or in an environment in which people are present. This means that systems can hurt people, especially when they fail or are used in an unusual way. Understanding customer usage, the environment, and potential failure modes is key to running a safety test. For consumer products, a classic example is small parts such as keys on a keyboard that can fall off or be plucked off and subsequently swallowed by a small child, resulting in choking.
Many portable computers contain batteries, which frequently include dangerous substances. Cadmium and nickel, for example, are potentially toxic metals found in some rechargeable batteries. Adequate care must be taken to ensure that these devices do not leak dangerous chemicals under foreseeable failure modes, and that warnings are included for safe disposal of the units after their life cycle is complete.
The NEBS test for telephony servers, telephone switches, and other devices to be located in central telephone offices specifies a fire test that actually involves taking a gas torch to various components on the system in a sealed chamber. (The tester should have a safety suit and an outside air supply for this test.) The resulting fumes are tested for toxicity, and the system is watched carefully for any signs of combustibility.