Which of the following can be a source of carbon monoxide during drainage work?

Carbon monoxide is a colorless, odorless gas that can be produced during the combustion of fuels. In the context of drainage work, petrol-driven generators are a significant source of carbon monoxide because they operate by burning fuel to generate power. When petrol is burned, carbon monoxide can be released as a byproduct, especially if the generator is not properly ventilated. This makes it crucial for workers in drainage to be cautious about using such equipment in enclosed or poorly ventilated areas to avoid the risk of carbon monoxide poisoning.

The other options mentioned, such as wooden tools, electric pumps, and concrete mixers, do not inherently produce carbon monoxide during their operation. Wooden tools do not involve combustion, electric pumps run on electricity without combustion emissions, and while some concrete mixers may be petrol-driven, many are electric, which would not release carbon monoxide. Understanding the sources of hazardous gases is vital for maintaining safety on the job site, especially during drainage operations.