Is there a standard for job sectors? Is there any sort of recognised standard (e.g. ISO) for grouping jobs into job sectors e.g. 'technology', 'emergency services'?

I asked this on StackOverflow here and they suggested this SE.

Would this be as close as I'm likely to get?
NAICS seems to be what you're getting at (http://www.census.gov/eos/www/naics/). This is the industry classification mechanism in North America. If you are interested in groups of workers' tasks as opposed to groups of establishments, you might be interested in occupation, which is the Standard Occupation Classification (SOC) system (http://www.bls.gov/soc/).