Choosing appropriate words for error levels

I develop an open-source, system monitoring tool, ServiceMon, and I'd really appreciate some help choosing the right words to use for a feature.

The state of the system that is being monitored is represented using a named severity level. The level changes when the number of errors, recorded within a given time period, breaches a particular threshold.

_{(source: rightcalc.com)}

I'd like to give each level a name, which will be used when configuring custom colours and threshold values. I'd ideally like to use meaningful adjectives - rather than cold, generic names like ErrorLevel1, ErrorLevel2, etc.

This is what I have so far:

Default Colour | Number of errors | Adjective
---------------------------------------------------
Green          | 0                | Operational
Yellow         | 1                | Temperamental
Orange         | 2-9              | Unstable
Light Red      | 10-99            | Critical
Dark Red       | 100 or more      | Dire

Do the words I've chosen seem appropriate? Can you think of any better alternatives?

Updated to elaborate on the primary use case

I envisage ServiceMon being primarily used as an "information radiator" - a permanent presence in a room that provides immediate visual notification of a system's state. Each ServiceMon instance is designed to be lightweight so that many can be tiled on one screen, with each one tracking a different system, or different aspect of the same system.  For example, where a system is being monitored for availability and responsiveness, I would envisage a separate instance running for each aspect, each with its own specific thresholds.