What grade of smoke is permitted in Omaha's boiler operation?

The correct response highlights that in Omaha's boiler operation, smoke emissions must not exceed grade 1 for more than 5 minutes per hour. This standard ensures that the emissions from boiler operations adhere to environmental regulations designed to maintain air quality and reduce pollution.

Maintaining smoke at grade 1 indicates relatively cleaner emissions, as this grade allows for only faint smoke, which is less likely to contribute to air pollution or health hazards. The restriction of a maximum of 5 minutes per hour reinforces the expectation of operating within strict limits, emphasizing the importance of sustained compliance to minimize environmental impact.

In this context, the other options do not align with the regulations. Accepting a darker grade of smoke, such as grade 2 at all times or grade 3 for longer periods, would likely heighten pollution and violate air quality standards. Allowing any grade of smoke for short durations would similarly undermine efforts to control environmental emissions, making it an inappropriate option.