In war on rats, cities try dry ice

It chills, it kills, it resolves urban ills

Some of America’s biggest metros have unleashed a chilling new killer in the urban war against rats: dry ice.

Sanitation officials recently launched a pilot program at four Chicago parks to test the effectiveness of dropping chunks of dry ice — frozen carbon dioxide — into burrows to try to suffocate rats as the dry ice sublimates from a solid to a gas.

Chicago began the experiment with dry ice in late August, following Boston, which became the dry ice pioneer when it launched its pilot in March, and New York City, which launched its test program in May.

“When I first brought up the idea, people around here thought I was cuckoo for Cocoa Puffs,” said Leo Boucher, assistant commissioner for Boston’s Inspectional Services, which consulted with Chicago as it launched its dry ice pilot. “But we all became believers. It works.”

The odorless gas in solid form — commonly used by stagehands to create an artificial fog effect and by merchants trying to keep perishables from spoiling — can be deadly to small animals at high concentrations.

This week, Chicago sanitation workers at one of the city’s oldest parks scooped chunks of smoking dry ice into a burrow before covering the entry and exit holes with dirt and newspaper to stop rats from escaping as the -109.3degree gas dissipated.

The asphyxiated dead rats then decompose in place and out of sight of city denizens who count the disease-carrying vermin among the vilest of indignities of urban living.

“We are seeing 60% fewer burrows in areas where we are using the dry ice,” said Charles Williams, Chicago’s streets and sanitation commissioner.

The asphyxiated dead rats then decompose in place and out of sight of city denizens who count the disease-carrying vermin among the vilest of indignities of urban living.