training, recruitment by hospitals for nursing staff, and increased pay in other occupations experiencing a labor shortage and not subject to government reimbursement limits. standards training and certification for a state specific list of qualification levels, see emergency medical responder levels by u.s. state. arriving at hospital the original lines that delineated an emt from a paramedic and a paramedic from a doctor are becoming increasingly blurred. skills that were once reserved for physicians are now routinely performed by paramedics, and skills once reserved for paramedics, such as defibrillation, are now routinely performed by basic emergency medical technicians (emts). however, there is wide variation among states, and even among counties within states, of what type of care providers at different levels are allowed to provide. in addition to these variations, some states and counties allow for add-ons, such as defibrillation or iv therapy, which enable workers at a lower level to learn and use additional skills that would not normally be within the scope of practice of their qualification level (for example, an emt is not generally permitted to start an iv, but after successfully completing an iv add-on course, he or she would then be able to do so.) add-on skills are generally more common in rural areas where definitive care is further away geographically and immediate interventions by emts are beneficial for patient care. a basic listing of qualification levels: emergency medical responder (emr): emrs, many of whom are volunteers, provide basic, immediate care including bleeding control, cpr, aed, and emergency childbirth. an emr, with the help of an emt, can assume care for a patient while that patient is being transported. emergency medical technician (emt): emt includes all emr skills, advanced oxygen and ventilation skills, pulse oximetry, noninvasive blood pressure monitoring, and administration of certain medications. advanced emergency medical technician (aemt): aemt includes all emt skills, advanced airway devices, intravenous and intraosseous access, blood glucose monitoring, and administration of additional medications. paramedic (see paramedics in the united states): paramedic is specialist health care provider, autonomous practitioner , providing advanced assessment and management skills, various invasive skills, and extensive pharmacology interventions, paramedic is the highest level in ems and its extension to the emergency physician . reciprocity - that is, recognition of one state's emt certification being valid in another state - between states is somewhat limited, and after 30 years of operation by the national registry of emergency medical technicians, only about 40 states provide unlimited recognition of the nremt certifications. in reality, there are at least 40 types of certification for ems personnel within the united states, and many of these are recognized by no more than a single state. this creates significant challenges for the career mobility of many ems providers, as they must often re-sit certification examinations each time they move from one state to another. medics in the united states safe at the hospital special events trauma care staffing ambulances in the united states must be staffed with a minimum of 2 personnel. the level of crew certification varies depending on the jurisdiction the ambulance is operating in. in most areas, the bare minimum is an emt to provide patient care and an emr to assist and drive the unit. this set-up would be classified as a basic life support unit (bls) due to the fact that the highest ranking provider cannot perform advanced life support (als) interventions. if patient condition warrants, an als provider may be summoned to assist and meet the ambulance en route to the hospital. other staffing combinations include one emt and one paramedic (the most common arrangement), or two paramedics, which are classified in most areas as an advanced life support unit (als). unlike in europe, emergency physicians do not regularly practice in the field, and only crew ambulances for specialty situations, such as extreme-low-weight infant transports, ecmo or cardiac bypass transports, or unusual situations such as crush injuries necessitating field amputation, or mass casualty/disaster situations. funding and manpower models ems is sometimes provided by volunteers. agencies that were once strictly volunteer have begun supplementing their ranks with compensated members in order to keep up with booming call volumes. as of 2004, the largest "private enterprise" provider of contract ems services in north america was american medical response, based in greenwood village, colorado. the second-largest us ems provider is rural/metro corporation, based in scottsdale, arizona; rural/metro corporation also provides ems services to parts of latin america. like amr, rural/metro provided other transportation services, such as non-emergency transport and "coach", or wheelchair, transportation. on october 28, 2015, amr announced that it had finalized the acquisition of rural/metro, forming the largest ems organization in the united states and employing nearly 25,000 individuals. many colleges and universities now also have their own ems agencies. collegiate ems programs vary somewhat from university to university; however, most agencies are fully staffed by student volunteers. agencies might operate what is called a quick response service (which does not transport patients but acts as a first responder to scenes) providing initial patient assessment and care, or they might operate certified ambulance services staffed with emts or paramedics. some groups limit services to within their campus, while others extend services to the surrounding community. services provided by college and university agencies may include ambulance services, mass-casualty incident response, aero-medical services, and search-and-rescue teams. while fire service in the us is rated based on iso classes, and fire insurance rates (casualty insurance) are based on those classes, ems does not receive ratings, nor are there corresponding monetary savings in health or life insurance policies. unlike fire and police protection, which are recognize as an essential services by the federal government, it has been left to local governments to determine if emergency medical services are necessary for their communities. this lack of federal recognition as an essential service has left emergency medical services grossly underfunded throughout the united states, leading to service closures and gaps in coverage for citizens throughout the country. medical control ems providers work under the authority and indirect supervision of a medical director, or board-certified physician who oversees the policies and protocols of a particular ems system or organization. both the medical director and the actions he or she undertakes are often referred to as "medical control". equipment and procedures are necessarily limited in the pre-hospital environment, and ems professionals are trained to follow a formal and carefully designed decision tree (more commonly referred to as a "protocol") which has been approved by medical control. this protocol helps ensure a consistent approach to the most common types of emergencies the ems professional may encounter. medical control may take place on-line, with the ems personnel having to contact the physician for direction delegation for all advanced life support (als) procedures, or off-line, with ems personnel performing some or all of their als procedures on the basis of protocols or "standing orders". the nhtsa curriculum remains the standard of care for ems organizations in the us. ambulances ambulances in the united states are defined by federal kkk-1822 standards requirements, which define several categories of ambulances. in addition, most states have additional requirements according to their individual needs. type i ambulances are based on the chassis-cabs of light duty pickup-trucks, type ii ambulances are based on modern passenger/cargo vans, referred to in the industry as vanbulances. type iii ambulances are based on chassis-cabs of light duty vans, ad (additional duty) versions of both type i and type iii designs are also defined. they include increased gvwr, storage and payload capacity. large american cities like new york and los angeles tend to have many distinct ambulance services, each with its own paint scheme and using all of the ambulance types mentioned above. pedestrians and drivers in such cities must be alert for ambulances of many shapes, sizes, and colors. most ambulances certified for emergency response in the u.s. are marked with the star of life for ready identification by the public. ems in the united states a typical type i ambulance a typical type ii ambulance a typical type iii ambulance a typical medium-duty ambulance with commercial truck chassis a typical military ambulance (us) based on hmmwv chassis medium-duty combination rescue/ambulance ambulances may be supplemented or supported by vehicles that lack the capacity to transport a patient. the most common of these vehicles is known by several names, including "response car". response cars are often equipped with much of the same equipment carried by an ambulance, but, since they are suvs or large cars, they are often faster and nimbler. response cars are staffed by one or more medical providers, and are used variously as a source of additional (or more skilled) manpower, as a supervisor's vehicle, or as a first response vehicle, enabling medical treatment to begin before the arrival of the ambulance. support vehicles in the united states typical heavy rescue unit a typical suv-based paramedic, known as a first responder unit, chase car or fly-car dispatch in the united states, there are as many methods of dispatching ems resources as there are approaches to providing ems service. in some larger communities, ems may be self-dispatching. where ems is operated as a division of the police or fire departments, it will generally be dispatched by those organizations. dispatching may occur through state-licensed ems dispatch centers, which are operated by one service but provide dispatch to several counties. in large centers, such as new york city, the statutory ems provider (in the case of nyc, the fdny) will dispatch not only their own vehicles, but also ems resources belonging to hospitals, private companies, and even volunteers, within their own community. the national emergency number in the united states is 9-1-1. the number works for all three emergency services. in most cases, a 9-1-1 call will be answered at a central facility, usually referred to as a public safety answering point, and operated, in most cases, by the police. the needs of the caller are identified, and the call is routed to the dispatcher for the emergency service(s) required. while some small communities continue to use "low-tech" approaches to dispatch, in many places in the u.s. the technology is quite advanced. advanced technologies in use may include electronic mapping, global positioning system (gps) or its first cousin automatic vehicle location (avl). the use of decision support software such as ampds is also common, as are surveillance "add-ons". as a result, many dispatchers are trained to a high level in their own right, triaging incoming calls by severity, and providing advice or medical guidance by telephone prior to the arrival of the ambulance or rescue squad on the scene. some are certified as emts or paramedics in their own states, and increasingly, are becoming certified as emergency medical dispatchers. response times there is no official federal or state standard for response times in the united states. response time standards frequently do exist in the form of contractual obligations between communities and ems provider organizations, however. as a result, there is typically considerable variation between standards in one community and another. new york city, for example, mandates a 10-minute response time on emergency calls, while some communities in california have moved response time standards to 12–15 minutes. it is generally accepted within the field that an "ideal" response time for emergency calls would be within eight minutes, ninety-percent of the time, but this objective is rarely achieved, and current research results question the validity of that standard. as call volumes increase and resources and funding fail to keep pace, even large ems systems such as pittsburgh, pennsylvania struggle to meet these standards. individuals who live in rural areas far from emergency services also may expect a longer wait due to the distance involved. this issue is further complicated by differing performance measurement methodologies. some services count response time beginning at the moment that the telephone call is answered and running until an ambulance or response resource arrives at the scene, while others measure only the time from the notification of ems personnel of the call, which is considerably shorter. another issue which arises in urban areas is that the response time "clock" almost universally stops when the unit arrives in front of the address; in large office or apartment buildings, actually accessing the patient may take several minutes