In February 2021, much of the United States experienced an unprecedented energy emergency caused by a severe winter weather system. Power producers of all sizes, from small hospitals to universities to utility companies, scrambled to interpret their air permits for both flexibility and restrictions. Was backup fuel operation limited? Did this situation qualify as an emergency under an air permit? How do the penalties for violating an air permit balance against a grid collapse? The questions raised by this recent emergency highlighted the need to plan, prepare and permit for the next inevitable major storm.

This winter weather emergency created a range of challenges for different types of power producers. The first step is to understand what limits exist for emergency equipment, and remember careful recordkeeping pays off when operating emergency equipment for any reason:

  • Emergency engines. Under federal regulations, emergency generators are limited to 100 hours per year for testing and maintenance. However, operation in an emergency is not limited when servicing your own facility. Some state regulations impose a 500-hours-per-year limit on operation of emergency generators in all situations. It is important to note that an emergency generator cannot sell power to the electric grid (during peak shaving). Providing power outside the facility is allowed under limited circumstances for up to 50 hours per year in coordination with the local transmission and distribution system. The federal regulations for reciprocating internal combustion engines, rules that all generators must adhere to, are some of the most confusing that EPA has ever published and require careful, repeated reading to interpret for each facility.

  • Anticipated emergencies. During the February 2021 storm, Southwest Power Pool issued several energy emergency alerts, from Levels 0 through 3, which provided documentation of the grid stability and warned of rolling brownouts. However, the EPA provided informal guidance that operation in anticipation of a storm, or other types of emergency situations, does not constitute an emergency and counts toward the 50 hours of operation that emergency generators can operate in nonemergency situations. The EPA has not yet issued a formal memo, also known as an applicability determination, on this type of situation. Until guidance is given, your facility can request that the EPA provide written, official guidance of when predicted winter storms, hurricanes or other natural disasters are considered emergencies for a plant. Power plants should ask the EPA to tie energy emergency alerts to the definition of emergency under federal regulations.

  • Backup fuel in boilers. At facilities that are minor sources of hazardous air pollutants, federal regulations classify boilers as gas-fired if they burn fuel oil for less than 48-hours-per-year. Requirements for oil-fired boilers are more complicated and require special energy assessments and tuneups. The 48 hours per year limit for fuel oil combustion applies only to hours run for the purposes of periodic testing, maintenance and operator training; it does not apply to operation during natural gas curtailment. Operation on fuel oil to save money, however, is not allowed for gas-fired boilers.

The second, more complicated step is to understand permit limitations that exist outside of emergency equipment:

  • Ton per year limits. Many facilities have ton per year limits for each pollutant that are specific to equipment. Changing these limits takes months. Operators must understand how hours of operation equate to tons of emissions to better manage anticipated and actual emergencies. Several days of emergency operation can be recouped by purposeful shutdowns later in the year. A considerable amount of discretion exists at the state and federal levels for enforcing violation of limits. While a hospital can reasonably anticipate a less strict consequence for exceeding a ton per year limit due to a storm event than a utility plant under the same circumstances, actual emission exceedances are always treated seriously. Emissions should be calculated each month on a 12-month rolling basis so that approaching limits can be identified and sufficient time can be provided to raise permit limits. Good communication with the local permitting authority and advance planning are key for emergency events.

  • Control equipment requirements. During the February 2021 storm, some utilities were limited not on fuel but on the demineralized water required for control devices. Under what circumstances, if any, does an emergency allow excessive pound per hour emissions due to control device malfunction? Guidance should be obtained from the permitting authority beforehand by brainstorming potential situations and solutions.

  • Fuel flexibility limits. Permits limit operation on backup fuel. Does it make sense to add liquefied natural gas as a second backup to natural gas and fuel oil?

  • Facility purpose. Some utility plants exist solely to provide peaking power or to operate for grid emergencies. Does the permit include the required flexibility? One recurring issue for utility plants with low-capacity factors involves routine maintenance and EPA enforcement of Prevention of Significant Deterioration (PSD) regulations. Many utilities have undergone maintenance projects that the EPA later decided should have obtained a major PSD permit, resulting in retrofit of expensive controls, large fines, or even plant shutdown. However, there is a way to reduce the risk of these potential PSD lookbacks by keeping records documenting advanced PSD netting calculations prior to routine maintenance.

An integrated team can help you analyze your situation for a customized solution to emergency operation, evaluating potential emergency situations and defining your allowable actions. Where your permit is too restrictive, such a team can work with the regulators to give you the flexibility you need to respond. But now is the time for action; permits take months to modify. Get the understanding and specific changes you need now, before the next weather event.


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Robynn is an associate environmental engineer at Burns & McDonnell with nearly 25 years of experience. Throughout her career, she has worked with industrial and utility clients to help acquire operating and construction air permits for projects.