Illinois Administrative Code
Title 83 - PUBLIC UTILITIES
Part 501 - STANDARDS OF SERVICE FOR GAS UTILITIES AND ALTERNATIVE GAS SUPPLIERS
Subpart D - GAS SERVICE STANDARDS
Section 501.530 - Heating Value

Each utility shall exercise in good faith all reasonable best efforts to maintain a consistent heating value for the natural gas it provides to its customers. A utility shall take what actions it deems necessary to avoid daily heating value fluctuations in excess of 5% for the gas it provides to individual customers. A utility may allow the daily heating value of gas delivered to its customer to fluctuate in excess of 5% when a failure to take the gas would result in a supply shortage, or when, for the purpose of meeting the requirements of a peak load or an emergency, a utility makes use of a reserve or emergency supply, such as liquefied petroleum gas.