The bigger the vehicle blocking, the better. You want mass between you and oncoming traffic. You want to assume that all approaching traffic will be unable to stop, is being operated by an inattentive driver or that the driver is medically impaired.
If you keep this mindset, you will remain alert to the dangers of moving traffic. Firefighters and EMS personnel do not operate in the unprotected 'upstream' side of a crash scene. All operations take place within the 'shadow', the protected downstream area created by the block from the large apparatus.
When the ambulance arrives at the scene, it must park in a safe 'downstream' position, a position on the departure side of the traffic flow. This requires the ambulance driver to pull past the initial blocking apparatus and around the crashed vehicles. The ambulance must stop at an angle that places the rear patient loading area as far away as possible from any moving traffic.
An upstream block enables the first-arriving officer to survey the scene from inside their vehicle. If the response is at night, the crew can use the headlights and vehicle-mounted spotlights for initial scene illumination. Additional units should either block further upstream from the crash or pull downstream into a safe and protected area. Additional emergency vehicles positioning at the scene will find locations on the downstream side of the scene the safest and most beneficial.
Expressway responses present unique challenges for initial traffic blocking. On any vehicle crash or fire call reported on any of the high-volume, limited-access expressways that run through the city of Plano, Texas for example, an additional fire department vehicle is dispatched on the initial call. Along with an engine company and ambulance, one of the department's tandem-axle ladder trucks also responds. For this crew, their primary function is to create an upstream block for the engine company and ambulance crew working the incident. This crew can also act as the "eyes in the back of the head" for those at the scene.
While other working personnel are intently concentrating on the action at the scene, the ladder truck serves as advance warning to approaching motorists of the situation ahead. This crew can also deploy traffic cones upstream of their apparatus to begin to 'taper' approaching traffic into one or more of the moving lanes of traffic. Should a problem motorist appear, one apparently oblivious to traffic control efforts, the ladder company can use their radio and air horn to warn fellow workers. Having someone dedicated to covering your rear can be a lifesaver!
Establishing the Hot Zone
The area of highest risk at a crash scene is where the crashed vehicles and the patients are located. This primary danger zone is commonly referred to as the 'hot zone', a familiar term used by hazardous materials teams. When no fuel, fire or spill hazards are present at a crash scene, the hot zone extends approximately 50 feet in all directions from the wreckage. The emergency vehicle initiating the first upstream block maintains this 50 foot hot zone spacing if possible. If one or more vehicles involved in the crash are burning, the hot zone distance increases to approximately 100 feet. The hot zone should be expanded whenever there are doubts about the safety and stability of a scene.
If the crashed vehicle is leaking gasoline, the fumes typically travel downhill and downwind to low-lying areas such as sewer drains, along curbs, ditches, and gullies. Because they must be evacuated and have all sources of potential ignition near them isolated, these low-lying areas become extended hot zones. Low areas should be avoided when positioning emergency vehicles or patients. Safe parking at a crash scene involving a utility company power pole requires vehicles and crews to avoid any area under overhanging transmission lines and near power transformers, which could short out. The hot zone should extend one intact pole beyond both affected poles when wires are down at a crash. Command personnel must quickly ascertain the stability of overhead wires, the damaged pole, adjacent power poles, and adjoining spans of transmission wires.