A clause-by-clause summary of the Ministerial Regulation Prescribing Odour Standards in Air from Factories B.E. 2568 (2025), effective 26 May 2025: revised definitions allowing instrument-based measurement, fence line and stack limits, measurement methods under Clauses 8 and 9, and the schedule of 24 factory categories.
The Ministerial Regulation Prescribing Odour Standards in Air from Factories B.E. 2568 (2025) was published in the Government Gazette, Volume 142, Part 21 Kor, page 7, on 27 March 2025, and took effect on 26 May 2025. It repeals the Ministerial Regulation Prescribing Standards and Methods for Inspecting Odour in Air from Factories B.E. 2548 (2005), which had been in force for more than twenty years [1][2].
Three changes matter most to operators: odour concentration may now be measured with analytical instruments in addition to the human nose, natural-rubber factories have been brought under control for the first time, and the stack limit for factories outside industrial zones has been relaxed. This article summarises the new regulation clause by clause, with comparison tables against the previous edition and the schedule of factory categories subject to odour measurement.
Why the regulation was revised
The note at the end of the regulation gives three reasons for its issuance [1].
- To update the standards and inspection methods for odour in air from factories so that they suit changed circumstances.
- To cover existing factory operations comprehensively, expanding the schedule from 23 categories to 24 by adding rubber production plants.
- To align with Section 56 of the Enhancement and Conservation of National Environmental Quality Act B.E. 2535 (1992), which requires authorities with statutory power to revise pollution control standards so that they are not lower than the source emission standards set by the Minister of Natural Resources and Environment [4].
Legal authority and effective date
The regulation was issued under Section 6, paragraph one, of the Factory Act B.E. 2535 (1992), as amended by the Factory Act (No. 2) B.E. 2562 (2019), together with Section 8 (5) of the Factory Act B.E. 2535, by the Minister of Industry [3]. It was given on 3 March 2025, signed by Mr Ekniti Promphan, Minister of Industry, and published in the Government Gazette on 27 March 2025.
- Clause 1 The regulation applies after the lapse of 60 days from the date of publication in the Government Gazette, that is, from 26 May 2025.
- Clause 2 The Ministerial Regulation Prescribing Standards and Methods for Inspecting Odour in Air from Factories B.E. 2548 is repealed.
Definitions compared: 2005 edition versus 2025 edition
Clause 3 of the new regulation revises several key definitions. The common thread is that analytical instruments are now expressly allowed for odour measurement alongside the human nose.
| Definition | Ministerial Regulation B.E. 2548 (2005) | Ministerial Regulation B.E. 2568 (2025) |
|---|---|---|
| Odour | A substance mixed in air that can be perceived by the human nose or an analytical instrument | A substance mixed in air that can be perceived by the human nose or measured by an analytical instrument |
| Odour concentration | A value expressing the odour condition, being the dilution ratio of an odorous air sample with clean air until the odour is almost imperceptible, analysed by sensory test under Clause 7 | A value expressing the odour condition, being the dilution ratio of an odorous air sample with clean air as perceived by the human nose, or the value measured by an analytical instrument |
| Industrial zone | An area designated for industrial land use under town planning law, or an industrial estate, or an industrial operation zone | An industrial estate or industrial operation zone, or an industrial land allocation project; the town planning criterion is removed |
| Odour sample | Defined as an air sample containing odour at the odour source under Clause 4 or Clause 7 | No longer defined |
Key observation. The 2025 edition adds instrument-based measurement of diluted air, opening the door to technologies such as the electronic nose (E-Nose). It removes the term “odour sample” from the definitions, and redefines “industrial zone” by dropping the town planning criterion while adding industrial land allocation projects.
Scope of application and the control principle
Clause 4 The regulation applies to factories of the type, kind or size prescribed by the ministerial regulation issued under Section 7, as listed in the schedule attached to this regulation, which sets out 24 categories (entries) of factories subject to odour measurement.
Clause 5 Factories under Clause 4 are prohibited from discharging odorous air from the factory unless the discharged air has been treated so that its odour concentration does not exceed the value prescribed in Clause 6 or Clause 7, as the case may be. Dilution must not be used to achieve compliance.
- Entries 1–22 and entry 24 → the standards in Clause 6 apply.
- Entry 23 (rubber factories) → the standards in Clause 7 apply, which differ from the first group.
Odour concentration standards
Clause 6 Air discharged from factories under Clause 4, entries 1 to 22 and entry 24, must have the following odour concentration.
- Located within an industrial zone: not exceeding 30 at the fence line or within the factory boundary, or not exceeding 1,000 at the factory stack.
- Located outside an industrial zone: not exceeding 15 at the fence line or within the factory boundary, or not exceeding 300 at the factory stack, per the text of Clause 6.
Clause 7 Air discharged from factories under Clause 4, entry 23 (rubber factories), whether located within or outside an industrial zone, must have an odour concentration not exceeding 30 at the fence line or within the factory boundary, or not exceeding 2,500 at the factory stack.
Summary comparison of odour standards
| Factory location | B.E. 2548 (2005) | B.E. 2568 (2025) | ||
|---|---|---|---|---|
| Fence line / within boundary | Factory stack | Fence line / within boundary | Factory stack | |
| Within an industrial zone | ||||
| Factory entries 1–22 and 24 | 30 | 1,000 | 30 | 1,000 |
| Factory entry 23 (rubber) | – | – | 30 | 2,500 |
| Outside an industrial zone | ||||
| Factory entries 1–22 and 24 | 15 | 300 | 15 | 1,000 |
| Factory entry 23 (rubber) | – | – | 30 | 2,500 |
What changed. First, factory entry 23 (rubber) is brought under control for the first time, with a fence line limit of 30 and a stack limit of 2,500 both inside and outside industrial zones. Second, the stack limit for entries 1–22 and 24 located outside industrial zones is relaxed from 300 to 1,000, while the fence line values remain unchanged.
Measurement methods and the transitional provision
Clause 8 Odour concentration under this regulation shall be measured by sensory test in accordance with the criteria and methods prescribed by the Minister and published in the Government Gazette. Measurement by methods other than the one in paragraph one, such as the electronic nose, shall likewise follow criteria and methods prescribed by the Minister and published in the Government Gazette. In practice this means the Department of Industrial Works must issue supporting criteria for both the sensory test and other methods.
Clause 9 (transitional provision) Pending the issuance of the criteria and methods prescribed by the Minister under Clause 8, the Ministerial Regulation Prescribing Standards and Methods for Inspecting Odour in Air from Factories B.E. 2548 and the orders issued under it shall apply to odour concentration measurement in the interim, until the criteria and methods under Clause 8 come into force.
In short, until the Department of Industrial Works announces the new criteria, measurement follows the 2005 procedures.
Schedule: the 24 factory categories subject to odour control
The schedule attached to the B.E. 2568 regulation lists 24 entries of factories required to measure odour, referring to the factory category numbers under the ministerial regulation issued pursuant to Section 7 of the Factory Act B.E. 2535. They are summarised below.
| Entry | Factory category | Type or kind of factory |
|---|---|---|
| 1 | 1 | Curing of tea leaves or tobacco leaves |
| 2 | 2 | Agricultural produce, such as boiling, steaming or drying plants or seeds; hulling seeds; baling jute or tobacco leaves; pressing or baling cotton and ginning kapok; storing or conveying crops in silos, warehouses or storehouses; grinding, milling or crushing plant parts; charcoal burning from coconut shells; culturing mushroom, orchid or bean sprouts; sifting, washing, sorting and grading; preserving produce by irradiation; egg incubation using incubators |
| 3 | 4 | Animals other than aquatic animals, such as slaughtering; preserving meat by baking, smoking, salting, pickling, drying or freezing; making finished food products from animal meat, fat or hide; extracting oil or fat from animals; packing meat in sealed containers; washing, dressing, shelling, boiling, steaming, frying or grinding animals; making egg products |
| 4 | 5 | Milk, such as pasteurising or sterilising; making fresh milk from milk powder and fat; condensed, powdered or evaporated milk; cream from milk; butter or cheese; fermented or cultured milk |
| 5 | 6 | Aquatic animals, such as making food from aquatic animals and packing in sealed containers; preserving aquatic animals; finished food products from aquatic animals, hide or fat; extracting oil or fat; washing, dressing, shelling, boiling, steaming, frying or grinding aquatic animals |
| 6 | 7 | Vegetable or animal oil, or animal fat, such as extraction; pressing or grinding the residue after oil extraction; hydrogenation; refining; making margarine, non-dairy cream or blended cooking oil |
| 7 | 8 | Vegetables, plants or fruits, such as making food or beverages and packing in sealed containers; preserving by stirring, drying, pickling or freezing |
| 8 | 9 | Seeds or tubers, such as milling, winnowing or polishing rice; making flour; grinding or milling seeds or tubers; finished food products from seeds; blending flour or seeds; peeling tubers or forming them into strips, slices or sticks |
| 9 | 10 | Flour-based food, such as bread or cake; biscuits or dry baked goods; flour-based food products in strand, pellet or piece form |
| 10 | 11 | Sugar from sugarcane, beet, stevia or other sweetening plants, such as syrup; brown sugar; raw or white granulated sugar; refining; lump or powdered sugar; glucose, dextrose, fructose; sugar from coconut or palmyra palm sap |
| 11 | 12 | Tea, coffee, cocoa, chocolate or confectionery, such as dried tea leaves or tea powder; roasting, grinding or milling coffee; cocoa powder; chocolate; chrysanthemum or ginger powder; fruit tablets; candied or preserved fruit; baking or roasting nuts or fruit kernels; chewing gum; sweets or toffee; ice cream |
| 12 | 13 | Seasonings or food ingredients, such as baking powder; food flavourings, tastes or colours; leavening flour; vinegar; mustard; salad oil; grinding or milling spices; chilli powder, pepper powder or curry paste |
| 13 | 15 | Animal feed, such as mixed or finished feed for livestock; grinding or milling plants, seeds, plant residue, animal meat, animal bone, animal hair or shells |
| 14 | 16 | Boiling, distilling or blending liquor |
| 15 | 17 | Production of ethyl alcohol, other than ethyl alcohol produced from sulphite liquor in pulp making |
| 17 | 19 | Malt or beer, such as making, milling or grinding malt, and brewing beer |
| 18 | 20 | Drinking water, non-alcoholic beverages, carbonated drinks or mineral water |
| 19 | 21 | Tobacco, compressed tobacco, shredded tobacco, chewing tobacco or snuff, such as drying tobacco leaves or stripping leaf stems; cigarettes or cigars; compressed, shredded or flavoured tobacco; snuff |
| 21 | 30 | Carding, bleaching, dyeing, polishing or finishing animal hair |
| 22 | 43 | Fertiliser, or substances for preventing or eliminating plant or animal pests (pesticides), excluding chemical fertiliser, such as making fertiliser or pesticide; storing or repacking; grinding soil or preparing other materials for blending |
| 23 | 52 | Rubber, specifically using natural rubber, such as making primary rubber sheets other than in a plantation or forest; cutting, blending, rolling into sheets or cutting natural rubber sheets; ribbed smoked sheet, crepe rubber, block rubber, latex; rubber products other than those under category 51, from natural or synthetic rubber |
| 24 | 92 | Cold storage plants |
Note: the source summary details 22 of the 24 entries and does not describe entries 16 and 20. Readers who need the complete schedule should consult the schedule attached to the regulation in the Government Gazette [1].
Observation. Entry 23, referring to factory category 52 for natural rubber, is newly added in the 2025 edition. It expands the schedule from 23 to 24 categories and is the only entry governed by the Clause 7 standards.
What operators should prepare
- Check whether your operation appears among the 24 entries in the schedule, and whether it falls under Clause 6 or Clause 7.
- Confirm whether your site is inside or outside an industrial zone under the new definition, which no longer refers to town planning law but does include industrial land allocation projects.
- Review your most recent measurement results against the fence line and stack limits in the table above.
- Track the criteria and methods the Minister will prescribe under Clause 8, since the 2005 procedures still apply in the meantime.
RE-VEAL provides in-depth odour source measurement and analysis. See our Odor Fingerprint monitoring and source analysis service or contact our team to assess your compliance with the new regulation.
References
[1] Ministerial Regulation Prescribing Odour Standards in Air from Factories B.E. 2568 (2025). Government Gazette, Vol. 142, Part 21 Kor, p. 7 (27 March 2025).
[2] Ministerial Regulation Prescribing Standards and Methods for Inspecting Odour in Air from Factories B.E. 2548 (2005).
[3] Factory Act B.E. 2535 (1992) and Factory Act (No. 2) B.E. 2562 (2019).
[4] Enhancement and Conservation of National Environmental Quality Act B.E. 2535 (1992), Section 56.
