The first-arriving crew will conduct triage. Pre-hospital emergency triage generally consists of a check for immediate life-threatening concerns, usually lasting no more than one minute per patient. In North America, the START system (Simple Triage and Rapid Treatment) is the most common and is considered the easiest to use. Using START, the medical responder assigns each patient to one of four color-coded triage levels, based on their breathing, circulation, and mental status. The triage levels are:

•   Immediate: Patients who have major life-threatening injuries, but are salvageable given the resources available
•   Delayed: Patients who have non-life-threatening injuries, but are unable to walk or exhibit an altered mental status
•   Walking Wounded: Patients who are able to ambulate out of the incident area to a treatment area
•   Deceased or Expectant: Used for victims who are dead, or whose injuries make survival unlikely.

Triage personnel do not conduct treatment, with the exception of:

• Airway maneuvers;
• Tourniquets for life-threatening hemorrhage; and
• Where allowed by local protocols, needle decompressions for tension pneumothoraces

Generally, a small group of responders, usually the first two or three crews on scene, can complete triage. When responding to a chemical, biological, or radiological incident, the first-arriving crew must establish safety zones prior to entering the scene. Safety zones include:

• The hot zone: The contaminated area
• The warm zone: The area where HazMat specialists will decontaminate patients and fellow responders
• The cold zone: The safe zone, where any personnel who are not specially trained in HazMat and do not have chemical or biological protection gear must remain at all times. Depending on the contaminant, the cold zone should be roughly 200–300 yards from the incident, uphill and upwind. It should also be at least 50 yards uphill and upwind from the warm zone.

These zones should be clearly identified and with engineer tapes, lights, or cones. All responders and patients must leave the hot zone in designated pathways into the warm zone where they will be decontaminated. A designated officer should be posted at the hot zone and warm zone to make sure all contaminated personal are treated and decontaminated before entering the cold zone.

Treatment

Once casualties have been triaged, they can be moved to appropriate treatment areas. Unless a patient is Green Tagged and ambulatory, litter bearers will have to transport patients from the incident scene to safer treatment areas located nearby. These treatment areas must always be within walking distance, and will be staffed by appropriate numbers of properly certified medical personnel and support people. The litter bearers do not have to be advanced medical personnel; their role is to simply place casualties onto carrying devices and transport them to the appropriate treatment area. Casualties should be transported in order of treatment priority: Red-Tagged patients first, followed by Yellow-Tagged, then Green-Tagged, and finally Black-Tagged. Each colored triage category will have its own treatment area. Treatment areas are often defined by coloured tarpaulins, flagging tape, signs, or tents. Upon arrival in the treatment area, the casualties are re-assessed and they are treated with the goal of stabilizing them until they can be transported to hospitals; transported to the morgue or medical examiners office; or released.

On-site morgue

Some mass-casualty incidents require an on-site morgue, for several reasons:

• To await transfer of these victims to a permanent morgue;
• When the deceased must be removed to access injured victims;
• To keep the deceased out of public sight and prevent heightening distress, fear, or panic in an already emotionally-charged scene

Most often, on-site morgues are set up on the far side of the incident, is in an enclosed area such as a temporary tent or nearby building.

Transport in MCI

The final stage in the pre-hospital management of a mass-casualty incident is the transport of casualties to hospitals for more definitive care. If an insufficient number of ambulances is available, other vehicles may transport patients, such as police cars, firetrucks, air ambulances, transit buses, or personal vehicles. As with treatment, transport priority is decided based on the severity of the patients injuries. Usually, the most seriously injured are transported first, with the least serious transported only after all the critical patients have been transported. However, in an effort to remove as many lightly injured civilians as possible, an incident commander may choose to have those least seriously injured transported to local hospitals or interim-care centres in order to provide more room for emergency personnel to work. It is also possible that lightly injured casualties will be transported first when access to those who are more severely injured will be delayed due to heavy or difficult rescue efforts. Ideally, once an MCI has been declared, a well-coordinated flow of events will occur, using three separate phases: triage, treatment, and transportation.