This paper reviews the current status of research as it is reflected in acceptable guidelines and limits for work in hot occupational environments. The worker engaged in job activities while in an uncomfortably hot or dangerously hot environment has two avenues leading to potential injury and illness. First the physiological responses can produce heat illness such as heat cramps, syncope, exhaustion or stroke. Secondly, the effects of heat on the worker’s perceptual motor and cognitive task performance can negatively affect the operations of controls, attention to warning signals and reaction-response times. Reduced performance in these types of tasks can lead to mishaps and injuries to the worker and/or other co-workers.