the condition of being protected from harm, and also refers to the control of recognized hazards in order to achieve an acceptable level of risk. When one operates where it is not feasible to avoid or remove hazards completely, safety implies that defences have been set up to recover from foreseeable incidents and to mitigate their consequences to an acceptable level. The level of accepted risk may be imposed by a regulatory body, an organisation performing an activity to which risk is connected, or the individual exposed to the risk. A distinction can be made between three types of safety: Environmental factors The underwater environment is alien to humans. When not actively hostile, it is unforgiving of errors, and some errors can escalate rapidly to a fatal conclusion. Many aspects of the underwater environment are static or predictable, others vary and may not be easily or reliably predictable, and must be managed as and when they occur. The reasonably predictable factors can be allowed for in the dive planning. Suitable equipment can be selected, personnel can be trained in its use and support provided to manage the foreseeable contingencies. When conditions are found to be other than predicted, plans may have to be changed. Sometimes conditions are better than expected, but other times they may be worse, and may deteriorate during the course of a dive to the extent that recovery becomes an emergency. Predictable and static environmental factors are conditions which should be considered in the dive plan. These include geographic factors, like depth, topography, access, tides and currents, normal temperature range and the local ecology. Variable environmental factors are the conditions that can change during a dive, like sea and weather conditions. Dive contingency plans should take into account the reasonably foreseeable variations based on forecasts and local knowledge. When there is no reliable local knowledge available, a wider range of variability should be considered. Unknown environmental factors are conditions which cannot be taken into account directly, but their reasonably foreseeable existence should be considered in risk assessment, and allowed for if there is a plausible risk. Equipment safety Two basic classes of equipment are used by divers: Equipment necessary to do the planned dive, and equipment required to do the task for which the dive is necessary. Recreational divers may not require equipment for a task, but it is quite common for them to use a camera,