uncommon, in a large urban centre, for an emd to manage and direct as many as 20 response resources simultaneously. it is the job of the emd to analyze the information and ensure that it leads to the right resource being sent to the patient in the shortest appropriate time. this requires a constant level of awareness of the location and status of each resource, so that the closest available and appropriate resource may be sent to each call. particularly in larger, urban settings, the mental demands and stress level may be comparable to those of an air traffic controller, and 'burn-out' rates may be quite high. this has been eased somewhat in recent years through the use of automatic vehicle locating (avl), permitting the emd to monitor the location and status of all assigned resources using a computer screen instead of by memory. the emds next priority is to provide and assist the layperson/caller with pre-arrival instructions to help the victim, using standardized protocols developed in cooperation with local medical directors. such instructions may consist of simple advice to keep the patient calm and comfortable or to gather additional background information for responding paramedics. the instructions can also frequently become more complex, providing directions over the telephone for an untrained person to perform cpr, for example. examples of emds guiding family members through assisting a loved one with the process of childbirth prior to the arrival of the ambulance are also quite common. the challenge for the emd is often the knowledge level of the caller. in some cases, the caller may have prior first-aid and/or cpr training, but it is often just as likely that the caller has no prior training or experience at all. this process may still consist of a symptom-based flip-card system, but is increasingly automated through computer aided dispatch software. the emd is generally also responsible for providing information support to the responding resources. this may include callbacks to the call originator to clarify information. it may involve clarifying the exact location of the patient, or sending a bystander to meet the ambulance and direct paramedics to the patient. it may also include requests from the ems crew to provide support resources, such as additional ambulances, rescue equipment, or a helicopter. the emd also plays a key role in the safety of ems staff. they are the first with the opportunity to assess the situation that the crew is responding to, will maintain contact on the scene in order to monitor crew safety, and are frequently responsible for requesting emergency police response to 'back up' paramedics when they encounter a violent situation. emds are often responsible for monitoring the status of local hospitals, advising paramedics on which hospitals are accepting ambulance patients, and which are on 're-direct' or 'divert'. in many cases, the emd may be responsible for notifying the hospital of incoming patients on behalf of the response resource crew. paramedics who are working on patients or driving an ambulance are rarely able to make a detailed telephone call. as a result, the emd will relay any advance notification regarding patient situation or status, once in transit. finally, the emd ensures that the information regarding each call is collected in a consistent manner, for both legal and quality assurance purposes. in most jurisdictions, all ems records, including both patient care and dispatch records, and also recordings of dispatch radio and telephone conversations, are considered to be legal documents. dispatch records are often a subject of interest in legal proceedings, particularly with respect to initial information obtained, statements made by the caller, and response times for resources. any or all may be demanded by a criminal court or civil court, a public inquiry, or a coroner's inquest, and may have to be produced as evidence. it is not uncommon in some jurisdictions for emds to be summoned to court, in order to provide evidence regarding their activities. as a result, there is frequently a legal requirement for the long-term storage of such information, and the specific requirements are likely to vary by both country and jurisdiction. additionally, medical directors will frequently rely on information provided by emds for the purpose of medical quality assurance for paramedics; in particular analyzing conversations between paramedics and dispatchers or physicians, analyzing the paramedic's actions and judgments in the light of the information that they were provided with. as a direct result of these two factors, there is a requirement for all call information to be collected and stored in a regular, consistent, and professional manner, and this too, will often fall to the emd, at least in the initial stages. work locations emd in austria the overwhelming majority of emds will perform their work in an ems dispatch centre. occasionally this may involve some 'site work', such as on-site dispatching for large special events, but this is somewhat rare. ems dispatching may be a single, independent process, or it may be a mixed function with one or more of the other emergency services. in some smaller jurisdictions, the ems, fire and police dispatch functions, and even the 9-1-1 system may be physically co-located, but with different specialist staff performing each function. such decisions are frequently made based on the sizes of the services involved, and their call volumes. while some jurisdictions are required, generally through economics or size, to provide a single public safety dispatch system, the three emergency services have requirements and procedures that are sufficiently different that wherever possible, independent dispatching is preferred. even in truly large, mixed (fire and ems) services, such as the new york city fire department, the functions and requirements are seen as sufficiently different that an independent dispatch function is maintained for each. the emergency services in question all have their own priorities, and while they are extremely important to each, those priorities often simply conflict too greatly to allow reasonable joint dispatch functions. to illustrate, in a scenario with a single dispatcher for both fire and ems: the truck officer on a fire apparatus is requesting additional resources for a working fire with a possibility of trapped people, and two paramedics are attempting to resuscitate a dying child, but require medical direction, which request gets priority? another important consideration is workload; in many jurisdictions the call volume of the ems system is 5-6 times as great as that of the fire department. asking fire service dispatchers to also dispatch ems resources, or vice versa, may exceed the capabilities of the dispatchers. even when joint dispatching is pursued by a community, the various types of dispatch functions to support ems, fire and police are so different that the dispatchers involved will require separate training and certification in each. increasingly, such public safety dispatch locations are becoming community owned and operated resources. as such, they tend to be co-located with other emergency service resources, as in a headquarters-type complex. such environments must strike a 'balance' between the high-tech requirements of the work, including large numbers of computers, telephone lines, and radios, and the psychological needs of the human beings operating them. the environment is frequently both high-performance and high-stress, and every measure must be taken to ensure as little ambient stress in the environment as possible. such issues are often the subject of careful design and also ergonomics. environmental colour choices, the reduction of ambient noise (and therefore stress) and the physical design of the seating and consoles used by the emd are all intended to reduce stress levels. supervisory staff also typically monitor staff carefully, particularly in high-performance environments, ensuring that rest and meal breaks are taken, and occasionally providing a 'time out' after a particularly difficult call. despite all of these measures, occupational stress is a significant factor for many emds, and the 'burnout' rate for those in these positions tends to be higher than other occupations. the role and certification of emergency medical dispatcher has its origins in the united states but is gradually gaining acceptance in many other countries. the position and credential are in widespread use in canada and the united kingdom. the acceptance and use of this position and credential are growing in the european union, in australia, and elsewhere. in many respects, the development of this position is a logical sequel to the incorporation of the emergency medical dispatch system by ems. together, naed and pdc often present themselves as the de facto standard in emd systems. however, the continued recognition given to alternative providers suggests that this approach is not universally accepted. and not all ems dispatch worldwide is conducted by emds. in some jurisdictions using the franco-german model of ems service delivery (samu in france, for example), a call for a medical emergency will not be processed by an emd, but generally by a physician, who will decide whether or not an ambulance will even be sent. training training for emds is required to meet a national standard curriculum, as outlined by the national highway traffic safety administration of the u.s. government. this training program may be offered by private companies, by community colleges, or by some large ems systems which are self-dispatching. the minimum length of such training is 32 classroom hours, covering such topics as emd roles and responsibilities, legal and liability issues in emd, national and state standards for emd, resource allocation, layout and structure of emd guidecards, obtaining information from callers, anatomy and physiology, chief complaint types, quality assurance & recertification and stress management. certification in cpr is not mandatory, but upon completion of the training, students are required to sit a certification examination. upon completion of the training and certification, emergency medical dispatchers are required to complete 24 hours of continuing dispatch education every two years, in order to maintain certification. this level of training and certification only satisfies the national curriculum, and in most cases, additional training will be required. additional training will have a local focus, and will deal with local geographical knowledge, dispatch procedures, local laws and service policy. additional training may be required to orient new emergency medical dispatchers to different forms of 9-1-1 telecommunication (if this will be a part of their job function). this may also include (depending on the jurisdiction) efd (emergency fire dispatching), epd (emergency police dispatching), etc (emergency telecommunication), ece (executive certification course), cmc (communication center manager), when such services are jointly operated. similar courses are also generally available in law enforcement dispatch (led), fire service dispatch (fsd), and public safety dispatch (psd), designed for those working in a multi-agency 9-1-1 call center that handles police, fire and ems dispatching. additional local training is likely to be required for the actual skill of dispatching. this may involve extensive 'drilling' on local geography, for example. large dispatch centres also tend to train staff in a graduated manner. some of the more sophisticated ems systems might actually have a teaching 'lab' complete with dispatch consoles, where the trainees can practice dealing with simulated calls, using exactly the same technologies that would be present in a real call centre. in other cases, or in addition to this 'lab' work in many cases, a graduated process of introduction and mentoring is used to develop an emd. this generally involves supervised introduction of tasks, from the lowest priority and least stressful, to the highest priority and most stressful. a typical pattern might begin with the candidate performing call reception, then progressing to the actual dispatching of non-emergency transfers, dispatching emergency calls during periods of low volume, dispatching emergency calls at periods of high volume, and so on. in high performance systems, the path to being left alone to run an emergency dispatch console during high volume periods may take months to travel. some ems dispatch centres also have designated communications training officers, who are the only people permitted to train or mentor new emd candidates. following the murder of denise amber lee in 2008, new laws are being considered in the state of florida regarding the training of all public safety telecommunicators including emds. one of the 9-1-1 calls relating to her abduction was allegedly mishandled. career paths in english-speaking countries emds come to their jobs from a variety of backgrounds. these might involve no prior experience at all, but are more likely to involve some other previous form of dispatching experience