Places of work come in a wide variety in terms of the activities which take place there, the materials used, the process involved and, ultimately, the hazards to health and safety that are present as a consequence of the work which occurs on site. The multitude of different risks to a person's safety and wellbeing means that health and safety training needs to be provided for employees so that they are aware of potential threats which may cause ill-health, injuries and possibly death in extremely serious incidents.
As to what are the "main" health and safety hazards, this will depend greatly upon the individual workplace. For example at a nuclear power plant radiation poisoning is likely to be one of the main health and safety risks in terms of the potential to cause harm to workers and everyone else in the vicinity including members of the public, but radiation will not be a consideration in a workplace such as an office. This is also where suitable health and safety training is required as there is little point in providing radiation safety training to office workers!
There are however health and safety risks which are a potential factor and danger to health in virtually any place of work. These include issues such as fire risk, mental health and wellbeing including stress, hazardous substances of varying strengths and hazard levels (minor irritants to toxic cancer-causing chemicals for instance), electrical safety, manual handling conditions, environmental impacts plus many more. Whilst there is a long list of possible dangers to health, safety and wellbeing of people, there are certain health and safety training courses available to provide attendees with knowledge regarding lots of common workplace risks, with the NEBOSH General Certificate being one of the primary examples. The syllabus of this NEBOSH course aims to cover and provide a general overview of those risks and dangers to health which are present in the majority of workplaces. Rather than attempt to cover every possible risk in every last detail (a task which would likely take many months at least!), the NEBOSH General Certificate course provides a fairly in-depth overview of the main hazards, and provides not only a lot of useful information for delegates to utilise when back in their work environment, but also provides a solid platform upon which to progress to higher or more specialised health and safety qualifications on a particular topic such as fire safety.