Any system failure which impedes the ability of a significant part of the department to get work done, particularly the failure of critical services should be considered an emergency. Failed redundant services which can easily be bypassed by moving to a different system, or outages which only affect one or two users, are not considered departmental emergencies.
For example, the File, Web and Mail services are critical - they should be available at all times. If any of these services appears to have crashed, contact systems staff immediately.
If your desktop or a compute node (e.g., Larc, Stretch, Power8) has crashed, and you can continue working by moving to another system, please do so, and notify root by mail. Please exercise some discretion, and do not contact systems staff at 2AM to report a printing emergency.