Performing simultaneous interpretation is indeed stressful. A conference interpreter must not let their concentration slip. When working in simultaneous mode, interpreters need to perform four key tasks at the same time: listening, analysing, speaking and monitoring their delivery. As they are rendering the words of the speaker, they are taking in and analysing his or her next utterances, in order to render them in turn. The process continues like this in a rolling fashion.
You might think that this alone would demand the full attention of the conference interpreter, but in reality he or she performs other tasks whilst live on mike, such as following the content of the speaker's PowerPoint presentation or consulting the meeting documents, looking up terminology on-line, making quick checks with their boothmate and operating their interpretation console (i.e. changing incoming and outgoing language channel, adjusting the incoming sound, and operating their microphone to tally with the speaker and with other interpreters).
To manage the stress factor and to ensure quality of service, the International Association of Conference Interpreters (AIIC) has set standards governing workload (maximum working hours), team strength (number of interpreters) and equipment for conference interpreters. AIIC standards are based on medical studies and are applied by Congrestolken. Generally, conference interpreters work in teams of two or more per booth, taking turns of about 30 minutes each, for a maximum of about three hours at a time.