If you see someone rifling through your compost bin, it may be a city employee.

The City of Calgary is sending staff to people's homes to check that they're composting according to the rules.

City staff have done such spot checks for a decade with blue and black bins. Now they're checking green bins for anything that could be dangerous to waste workers, such as propane tanks or scrap metal.

"In the 10 years that we've been doing this, we have not used a fine for a spot check," Sharon Howland told the Calgary Eyeopener on Friday morning.

"It's an education-first approach. We want Calgarians to use the cart correctly so that our workers aren't getting hurt at the different facilities where this material goes to. It's not about punishment. We just want to correct the behaviour."

In fact, the city says it has never issued a fine for inappropriately sorting waste materials, whether the issue was caught by a spot check, neighbour or waste collector.

How to make a DIY compost bin liner:

Step by step tutorial shows how to repurpose flyers or newspapers for your kitchen compost pail0:34

Composting service has been available in four Calgary communities since 2012. Collection rolled out across the city in July.

If your bin is found with any hazardous or unacceptable materials, the city may tag it with a note and turn the bin sideways so the trucks can't collect it.

Repeat offenders may see a letter in the mail — or even a compost educator knocking on their door.

No plastic bags

The most common thing officers find is when residents use plastic bags to hold compost, instead of the approved compostable ones, which can be bought at many grocery stores, Howland said.

The strangest thing she's ever found was a giant wooden Tiki head in the blue cart.

"Probably not the best cart for that to go in," she said. "We would actually suggest donating that. Use Kijiji or take it down to one of the thrift stores."

If you have any questions about sorting your household waste, the city has resources online.