Statutory guidance

SR2018 number 4: Specified Generator, Tranche B low risk, between 0 to less than or equal to 20 MWth, operated less than 500 hours a year

Updated 26 February 2026

Applies to England

The Environmental Permitting (England & Wales) Regulations 2016

Introductory note

This introductory note does not form a part of these standard rules.

These rules will permit:

• Tranche B specified generators (that may include medium combustion plant) with an individual unit net rated thermal input of less than or equal to 20 MWth burning only natural gas, hydrogen,  ultra-low sulphur diesel (10 ppm sulphur) or gas oil substitutes.

When referred to in an environmental permit these rules will allow the operator to operate one or more of these combustion plant, operated for less than 500 hours a year which are gas or abated liquid fuel engines which may be providing a balancing service in the peaking market to the National Grid providing:

• the total aggregated net rated thermal input of all combustion plant is less than or equal to 20 MWth
• each emission point has a minimum stack height of 3m

All combustion plant must meet the following location criteria:

• The minimum distance from any point source emission to a sensitive human receptor is 150m
• The minimum distance from any point source emission to a protected habitat is 600m for engines burning natural gas, ultra-low diesel (10ppm sulphur) or gas oil substitutes
• The minimum distance from any point source emission to a protected habitat is 600m for engines burning hydrogen as a primary fuel which are also new Medium Combustion Plant (MCP)
• The minimum distance from any point source emission to a protected habitat is 700m for engines burning hydrogen as a primary fuel which are also existing MCP or where generators less than 1 MWth are used to aggregate the specified generator capacity
• The background NO₂ concentration at sensitive human receptors is less than or equal to 31 µg/m³
• Combustion plant shall not be located in an Air Quality Management Area declared for NO₂

Different requirements apply where the Generator includes new medium combustion plant or existing medium combustion plant with a net rated thermal input greater than 5 MWth. See Table 3.2.

Decarbonisation readiness requirements in accordance with Schedule 25C of The Environmental Permitting (England and Wales) Regulations SI 2016 No.1154 apply to new or substantially refurbished plant permitted under this rule set from 28 February 2026.

Words and expressions used in this introductory note and these standard rules shall have the meanings given in section 4.4, as appropriate.

End of introductory note.

Rules

1. Management

1.1 General management

1.1.1 The operator shall manage and operate the activities:

(a) in accordance with a written management system that identifies and minimises risks of pollution, so far as is reasonably practicable, including those risks arising from operations, maintenance, accidents, incidents, non-conformances and those drawn to the attention of the operator as a result of complaints; and

(b) using sufficient competent persons and resources.

1.1.2 Records demonstrating compliance with rule 1.1.1 shall be maintained.

1.1.3 Any person having duties that are or may be affected by the matters set out in these standard rules or the permit shall have convenient access to a copy of the permit and the rules.

2. Operations

2.1 Permitted activities

2.1.1 The operator is only authorised to carry out the activities specified in table 2.1.

Table 2.1 - Activities

Activity reference	Description of specified activity	Limits of specified activity
Specified Generator Tranche B	Specified Generator burning only natural gas, hydrogen, ultra-low sulphur diesel (10 ppm sulphur) or gas oil substitutes	Capacity - total net rated thermal input of all engines less than or equal to 20 MWth Limited hours – maximum annual hourly operation of 500 hours Minimum distance from any point source emission to a sensitive human receptor is 150m Minimum distance from any point source emission to any protected habitat is 600m for engines burning natural gas, ultra-low sulphur diesel (10ppm sulphur) or gas oil substitutes as the primary fuel. The minimum distance from any point source emission to a protected habitat is 600m for engines burning hydrogen as a primary fuel which are also new MCP The minimum distance from any point source emission to a protected habitat is 700m for engines burning hydrogen as a primary fuel which are also existing MCP or where generators less than 1 MWth are used to aggregate the specified generator capacity Stack height – minimum 3m Background NO2 concentration less than or equal to 31 µg/m3 at any human sensitive receptor. The Specified Generator shall not be located within an AQMA declared for NO2
Medium Combustion Plant (MCP)	Medium Combustion Plant burning natural gas, hydrogen, ultra-low sulphur diesel (10 ppm sulphur) or gas oil substitutes as a Specified Generator	Net rated thermal input of individual combustion plant greater or equal to 1 MWth and less than 20 MWth (The limits listed above for Specified Generator also apply to MCPs)

2.2 The site

2.2.1 The Specified Generator activities shall only be carried out at the address in this permit where the plant is located.

2.2.2 Where MCP’s are operated as part of the Specified Generator, only those MCPs listed in the permit can be operated at the site. No MCP shall be operated beyond the site of the grid reference specified for it in the permit in Appendix A.

2.4 Operating techniques

2.4.1 The activities shall be operated using the techniques and, in the manner, described in the following sub-paragraphs.

Technique 1

The combustion plant must be operated in accordance with the manufacturer’s instructions and records must be made and retained to demonstrate this.

Technique 2

The operator must keep periods of start-up and shut down of the combustion plant as short as possible.

Technique 3

There is no persistent emission of ‘dark smoke’ as defined in section 3(1) of the Clean Air Act 1993.

Technique 4

The stack must be vertical and unimpeded by cowls or caps.

Technique 5

Where secondary abatement is required to ensure compliance with the NOx ELV it must be met within 10 minutes from when the combustion plant commences operation and 20 minutes when the generator was a Tranche A and is now a Tranche B.

2.5 Decarbonisation readiness 

2.5.1 Where an application relating to this permit included a statement that the CCR conditions or HCR conditions are met, the operator shall: 

(a) keep a site-specific decarbonisation readiness report;  

(b) review and update the report at intervals not exceeding 2 years;  

(c) notify the Environment Agency where there is a change in the type of technical assessment for any of the plant included in the report; 

(d) provide a copy of the report or findings of any review to the Environment Agency on request; and 

(e) ensure that the CCR conditions or the HCR conditions are met. 

3. Emissions and monitoring

3.1 Emissions to air

3.1.1 There shall be no point source emissions to air, except from the applicable sources and emission points listed in Appendix A.

3.1.2 The point source emissions to air shall not exceed the applicable  emission limit values given in tables 3.1 and 3.2.

3.1.3 The emission limits for natural gas given in Tables 3.1 and 3.2 can be applied to fuel blends of natural gas and hydrogen, when the relevant percentage multiplier given in Table 3.3 has been applied to them.

Table 3.1 Point source emissions to air – emission limits and monitoring requirements (applicable to each generator)

Parameter	Combustion technology and fuel type	Emission limit mg/Nm3	Monitoring frequency	Monitoring standard or method
Oxides of Nitrogen (NO and NO2 expressed as NO2)	Abated liquid fuel engine	190	Every 3 years	Monitoring requirements are defined at a temperature of 273.15 K, a pressure of 101.3 kPa and after correction for the water vapour content of the waste gases at a standardised O2 content of 15% for engines
Oxides of Nitrogen (NO and NO2 expressed as NO2)	Natural Gas engine	190	Once within 4 months of the issue date of the permit or the date when the generator is first put into operation, whichever is later	Monitoring requirements are defined at a temperature of 273.15 K, a pressure of 101.3 kPa and after correction for the water vapour content of the waste gases at a standardised O2 content of 15% for engines
Oxides of Nitrogen (NO and NO2 expressed as NO2)	Hydrogen engine	260.3	Once within 4 months of the issue date of the permit or the date when the generator is first put into operation, whichever is later	Monitoring requirements are defined at a temperature of 273.15 K, a pressure of 101.3 kPa and after correction for the water vapour content of the waste gases at a standardised O2 content of 15% for engines

Table 3.2 Point source emissions to air – emission limits and monitoring requirements (applicable to each generator that is also a medium combustion plant)

Parameter	Combustion Technology and fuel type	Emission Limit mg/Nm3	Monitoring frequency	Monitoring standard or method
Oxides of Nitrogen (NO and NO2 expressed as NO2)	Abated liquid fuel engine	190	Every 3 years	Monitoring requirements are defined at a temperature of 273.15 K, a pressure of 101.3 kPa and after correction for the water vapour content of the waste gases at a standardised O2 content of 15% for engines
Carbon Monoxide (CO)	Abated liquid fuel engine	No limit	Every 3 years	Monitoring requirements are defined at a temperature of 273.15 K, a pressure of 101.3 kPa and after correction for the water vapour content of the waste gases at a standardised O2 content of 15% for engines
Oxides of Nitrogen (NO and NO2 expressed as NO2)	Natural Gas engine	190	Every 3 years	Monitoring requirements are defined at a temperature of 273.15 K, a pressure of 101.3 kPa and after correction for the water vapour content of the waste gases at a standardised O2 content of 15% for engines
Carbon Monoxide (CO)	Natural Gas engine	No limit	Every 3 years	Monitoring requirements are defined at a temperature of 273.15 K, a pressure of 101.3 kPa and after correction for the water vapour content of the waste gases at a standardised O2 content of 15% for engines
Oxides of Nitrogen (NO and NO2 expressed as NO2)	Hydrogen engine	260.3	Every 3 years	Monitoring requirements are defined at a temperature of 273.15 K, a pressure of 101.3 kPa and after correction for the water vapour content of the waste gases at a standardised O2 content of 15% for engines
Carbon Monoxide (CO)	Hydrogen engine	N/A	Every 3 years	Monitoring requirements are defined at a temperature of 273.15 K, a pressure of 101.3 kPa and after correction for the water vapour content of the waste gases at a standardised O2 content of 15% for engines

Table 3.3 ELVs for fuel blend of hydrogen with natural gas

Substitution of hydrogen (% v/v)	Pollutant ELV expressed as a percentage of the analogous natural gas ELV
0 to 20%	100%
Greater than 20% to 50%	107%
Greater than 50% to 75%	115%
Greater than 75% to 90%	125%
Greater than 90% to 95%	130%
Greater than 95% to 100%	137%

3.2 Monitoring

3.2.1 The operator shall, unless otherwise agreed in writing by the Environment Agency, undertake monitoring for the parameters, at the locations and at not less than the frequencies from the issue date of the permit, specified in the tables 3.1 and 3.2.

3.2.2 The operator shall, if notified in writing by the Environment Agency, undertake additional monitoring for the parameters and at the locations specified in tables 3.1 and 3.2.

3.2.3 In the case of New Medium Combustion Plant the first monitoring measurements shall be carried out within four months of the issue date of the permit or the date when the combustion plant is first put into operation, whichever is later.

3.2.4 The stack emissions monitoring programme shall be carried out in accordance with the guidance ‘monitoring stack emissions: low risk MCPs and specified generators’ or using monitoring equipment, techniques, personnel and organisations with MCERTS certification or MCERTS accreditation (as appropriate), unless otherwise agreed in writing by the Environment Agency.

3.2.5 Monitoring shall not take place during periods of start up or shut down.

3.2.6 Where secondary abatement is required to ensure compliance with the NOx ELV monitoring shall start 10 minutes from when the generator commences operation and 20 minutes when the generator was a Tranche A and is now a Tranche B.

3.2.7 The operator shall maintain records of all monitoring including records of the taking and analysis of samples, instrument measurements (periodic and continual), calibrations, examinations, test and surveys and any assessment or evaluation made on the basis of such data.

4. Information

4.1 Records

4.1.1 All records required to be made by these standard rules shall:

(a) be legible;

(b) be made as soon as reasonably practicable;

(c) if amended, be amended in such a way that the original and any subsequent amendments remain legible, or are capable of retrieval, and

(d) be retained, unless otherwise agreed in writing by the Environment Agency, for at least 6 years from the date when the records were made.

4.1.2 The operator shall maintain convenient access, in either electronic or hard copy, to the records, plans and management system required to be maintained by these rules.

4.1.3 The operator shall maintain a record of the type and quantity of fuel used and the total annual operating hours for each generator.

4.1.4 The operator shall maintain a record of any events of non-compliance and the measures taken to ensure compliance is restored in the shortest possible time.

4.2 Reporting

4.2.1 The operator shall send all reports and notifications required by these standard rules to the Environment Agency using the contact details supplied in writing by the Environment Agency.

4.2.2 Where monitoring is undertaken in accordance with rule 3.2.1, 3.2.2 and where required 3.2.3, the operator shall submit to the Environment Agency within 28 days of undertaking the monitoring, using the form made available for the purpose, the information specified on the form relating to that monitoring.

4.3 Notifications

4.3.1 In the event:

(a) of a breach of any permit condition the operator must immediately:

(i) inform the Environment Agency, and

(ii) take the measures necessary to ensure that compliance is restored within the shortest possible time

(b) of a breach of any of the standard rules which causes a significant degradation of local air quality, the operator must immediately suspend the operation of the activities or the relevant part of them until compliance with the rules has been restored.

4.3.2 Any information provided under standard rule 4.3.1 shall be confirmed in writing within 24 hours.

4.3.3 Where the operator is notified by the Environment Agency under rule 3.2.2, to undertake monitoring at frequencies not otherwise specified in Tables 3.1 and 3.2, the operator shall provide, at least 14 days prior to the monitoring being carried out, details of when the monitoring is to take place.

4.3.4 The Environment Agency shall be notified within 14 days of the occurrence of the following matters except where such disclosure is prohibited by Stock Exchange rules:

(a) Where the operator is a registered company:

(i) any change in the operator’s trading name, registered name or registered office address, and

(ii) any steps taken with a view to the operator going into administration, entering into a company voluntary arrangement or being wound up

(b) Where the operator is a corporate body other than a registered company:

(i) any change in the operator’s name or address, and

(ii) any steps taken with a view to the dissolution of the operator

(c) In any other case:

(i) the death of any of the named operators (where the operator consists of more than one named individual)

(ii) any change in the operator’s name(s) or address(es), and

(iii) any steps taken with a view to the operator, or any one of them, going into bankruptcy, entering into a composition or arrangement with creditors, or, in the case of them being in a partnership, dissolving the partnership

4.3.5 The operator shall notify the Environment Agency, as soon as is practicable, in writing of any change of medium combustion plant Annex I information.

4.4 Interpretation

4.4.1 In these standard rules the expressions listed in this section shall have the meanings given.

4.4.2 In these standard rules references to reports and notifications mean written reports and notifications, except where reference is made to notification being made ‘immediately’, in which case it may be provided by telephone.

‘Accidents’ means an accident that may result in pollution.

‘Air quality management area’ means that defined in the Environment Act 1995, Part VI, 83.(1) as amended.

‘Annex I’ means Annex I of EU Directive 2015/2193 on Medium Combustion Plant

‘Appendix A’ means Appendix A as attached to the permit. 

‘Background NO2 concentration’ means a representative value for the background concentration for NO2 at your location, calculated from Local Authority ambient monitoring or background maps produced by Defra: https://laqm.defra.gov.uk/review-and-assessment/tools/background-maps.html

‘CCR’ means carbon capture readiness 

‘CCR conditions’ has the meaning set out in paragraph 4 of Schedule 25C of The Environmental Permitting (England and Wales) Regulations SI 2016 No.1154 

‘Change in type of technical assessment’ means changing to a CCR technical assessment or changing to a HCR technical assessment, both of which are defined in Paragraph 3 of Schedule 25C of The Environmental Permitting (England and Wales) Regulations SI 2016 No.1154. 

‘Decarbonisation readiness report’ has the meaning as defined in paragraph 3(2) of Schedule 25C of The Environmental Permitting (England and Wales) Regulations SI 2016 No.1154 

‘EP Regulations’ means The Environmental Permitting (England and Wales) Regulations 2016 SI No.1154 and words and expressions used in these rules or the permit which are also used in the Regulations have the same meanings as in those Regulations.

‘Existing MCP’ means MCP with a net rated thermal input equal to or greater than 1MWth and less than 20MWth which was put into operation before 20 December 2018.

‘First put into operation’ means the date when fuel is first combusted in the MCP. This can be during initial on-site commissioning but does not include conformity testing at the place of manufacture of the plant. 

‘Gas engine’ means a spark ignition reciprocating engine or compression ignition engine.

‘Gas oil substitutes’ includes hydrotreated vegetable oil and other liquid fuels approved as being equivalent to gas oil by the Environment Agency, as published in our Medium combustion plant (MCP): comply with emission limit values guidance.

‘HCR’ means hydrogen conversion readiness 

‘HCR conditions’ has the meaning set out in paragraph 5 of Schedule 25C of The Environmental Permitting (England and Wales) Regulations SI 2016 No.1154 

‘Liquid fuel engine’ means an internal combustion engine which operates according to diesel cycle and uses compression ignition to burn fuel. 

“MCERTS” means the Environment Agency’s Monitoring Certification Scheme. 

‘Monitoring stack emissions, low risk MCPs and specified generators’ refers to the guidance with that title published on GOV.UK and last updated on 04 June 2024, or any subsequent version which makes only editorial changes. 

‘New Medium Combustion Plant’ Any single combustion plant with a net rated thermal input equal to or greater than 1 MWth and brought into operation on or after the 20 December 2018.

‘Operating hours’ means the time, expressed in hours, during which the combustion plant is operating and discharging emissions into the air, excluding start-up and shut-down periods. 

‘Primary fuel’ means where there is a blend of natural gas and hydrogen the primary fuel is defined as the component that constitutes more than 50% of the blend. If equal, then use natural gas as the primary fuel.

‘Protected habitat’ means Special Areas of Conservation (SAC), Special Protection Areas (SPA), Ramsar Sites, Marine Conservation Zones (MCZ) and Sites of Special Scientific Interest (SSSI). 

‘Specified generator’ means an individual generator or a number of generators on the same site, operated by the same operator, for the purpose of generating electricity. 

‘Sensitive human receptors’ means locations where there is relevant public exposure. Relevant public exposure is where members of the public have access, are regularly present and can be exposed for a significant portion of the averaging time of the standard. The standards do not apply where health and safety at work provisions exist and where members of the public do not have access.

‘Year’ means calendar year ending 31 December.

End of standard rules.