Generally perceived as pay per use emergency services, domestic emergency services are small, medium or large businesses who tend to emergencies within the boundaries of licensing or capabilities. These tend to consist of emergencies where health or property is perceived to be at risk but may not qualify for official emergency response. Domestic emergency services are in principal similar to civil emergency services where public or private utility workers will perform corrective repairs to essential services and avail their service at all times; however, these are at a cost for the service.  
The key principle taught in almost all systems is that the rescuer, be they a lay person or a professional, should assess the situation for danger. The reason that an assessment for danger is given such high priority is that it is core to emergency management that rescuers do not become secondary victims of any incident, as this creates a further emergency that must be dealt with. A typical assessment for danger would involve observation of the surroundings, starting with the cause of the accident (e.g., a falling object) and expanding outwards to include any situational hazards (e.g., fast moving traffic) and history or secondary information given by witnesses, bystanders or the emergency services (e.g., an attacker still waiting nearby). Once a primary danger assessment has been complete, this should not end the system of checking for danger, but should inform all other parts of the process. If at any time the risk from any hazard poses a significant danger (as a factor of likelihood and seriousness) to the rescuer, they should consider whether they should approach the scene (or leave the scene if appropriate).