Dry ice sieving separates cannabis resin heads from dried plant material using cold of about −78.5 °C instead of water or solvent. It is fast and cheap, but it carries two physical hazards: carbon dioxide gas that can suffocate you, and cold that can burn skin and eyes. This part covers those hazards, why mouldy plant material should never go in, the Thai legal position, and a checklist for a working session.
Much of the method comes from a home grower’s manual on resin separation, called “the manual” below. The manual plays down the gas hazard and accepts mouldy and mite-infested input. Both points are corrected here.
Legal warning. In Thailand, separated cannabis resin will in practice contain far more than 0.2% THC. Cannabis extracts above 0.2% THC are Category 5 narcotics, and producing, possessing or supplying them without a licence is a criminal offence. This article describes processing in licensed or research settings and is not a guide to personal production.
This is Part 2. Part 1: Dry Ice, Dry Sift and Charas: Mechanical Trichome Separation and Its Real Safety Profile
7. Safety
7.1 Carbon dioxide can suffocate you
Dry ice is frozen carbon dioxide (CO₂). At room temperature it turns straight from solid to gas without melting, a change called sublimation. Each kilogram of dry ice becomes roughly 540 litres of CO₂ gas. A 0.5 kg run releases about 270 litres, and a 1 kg run about 540 litres, into the space where you work.
Raised CO₂ levels cause headache, dizziness, confusion, shortness of breath, loss of consciousness and death. CO₂ is dangerous at levels that have not yet lowered oxygen enough to set off an oxygen-shortage alarm. So an oxygen alarm alone does not protect you. CO₂ is heavier than air and collects at floor level and in low spaces.
- Ventilation is required. Work in a processing area with a running extraction fan, or outdoors. Never work in a small closed room.
- Never work in a cold room, a refrigerator, a vehicle, a lift or any other enclosed space.
- Never use a sealed container. Gas pressure can burst a container violently. Do not keep leftover dry ice in a sealed cooler box, and avoid glass containers.
- If you run this process regularly, put a CO₂ monitor in the processing area.
Translator’s note: Many Thai grow and processing rooms are kept closed so the air conditioner can work. A closed air-conditioned room is exactly the wrong place for dry ice. Work outdoors in shade or in a room with an extraction fan running, and keep the gas away from floor-level spaces where it can pool. CO₂ is also used to raise yields in grow rooms; see CO₂ enrichment for how gas levels are managed there.
What to do: Before the first run, choose the work area and check that air is actually moving out of it. If you will run dry ice more than occasionally, buy a CO₂ monitor first.
7.2 Cold burns
At about −78.5 °C, dry ice freezes skin and tissue very quickly.
- Loose-fitting insulated cryogenic gloves (gloves made for handling extremely cold materials) that you can pull off fast. Never use bare hands.
- Safety glasses with side shields. Wear goggles and a face shield when you break up dry ice, which is exactly what the hammer step does.
- Long trousers and closed shoes. Check gloves and tools before use, and never use wet or damaged equipment.
The manual gives one warning that is worth repeating: the metal can becomes extremely cold, and it is the part people grab without thinking. Keep your gloves on for the whole shaking stage.
What to do: Put on gloves before you touch the can, and eye protection before you pick up the hammer. Leave both on until all the dry ice is gone.
8. Plant material: where this article disagrees with the manual
The manual says flower infested with spider mites, and mouldy flower, can be used, because the mesh filters out the mites. Its writer says he has processed and consumed resin from flower heavily infected with powdery mildew, without problems. This article does not repeat that advice, and the published evidence is against it.
A 2023 review by Gwinn and colleagues reports that more than 100 fungal species have been found on cannabis flowers. Some groups of fungi can produce toxins, called mycotoxins. The groups of concern include Aspergillus (aflatoxins, ochratoxin A), Penicillium (ochratoxin A, citrinin, patulin), Fusarium (trichothecenes, fumonisins, zearalenone) and Mucor. For how these fungi behave in Thailand’s rainy season, see mycotoxins on cannabis flower.
The same review describes case reports of pulmonary aspergillosis, a lung infection caused by Aspergillus, in cannabis users. The patients had HIV, type 1 diabetes, or cancer or other conditions that weaken the immune system. The review also warns that heat from smoking or vaping should kill spores but “may be insufficient to render all spores nonviable” – in other words, some spores may survive.
- Gwinn KD, Leung MCK, Stephens AB, Punja ZK. Fungal and mycotoxin contaminants in cannabis and hemp flowers: implications for consumer health and directions for further research. Frontiers in Microbiology 2023;14:1278189. doi:10.3389/fmicb.2023.1278189
A 2020 study by Benedict and colleagues used US health-insurance claims records. It found that cannabis users were 3.5 times more likely to have a fungal infection than non-users (adjusted odds ratio 3.5, 95% confidence interval 2.6–4.8). Because the data are claims records, the study shows a link but does not prove that cannabis use causes the infections.
- Benedict K, Thompson GR, Jackson BR. Cannabis Use and Fungal Infections in a Commercially Insured Population, United States, 2016. Emerging Infectious Diseases 2020;26(6):1308–1310. doi:10.3201/eid2606.191570
The manual’s argument also misses two points.
- Mycotoxins are stable chemicals. Killing the fungus does not remove them. Mechanical separation concentrates them together with the resin.
- One person’s experience is no evidence of safety for material that could reach a patient with a weak immune system.
The position here: do not process visibly mouldy material. Under GACP (the certification standard for cannabis farms, see Good Agricultural and Collection Practice) or GMP (the manufacturing standard, see EU-GMP and PIC/S GMP), contaminated material is rejected, and passing a mycotoxin test is a condition for releasing a batch. The mesh does keep out mites and their debris. Even so, mite-infested material is still unsuitable for anything supplied to others.
The manual is right on one point: better plant material gives better resin. Sugar leaf (the small resin-covered leaves in the bud), seeded flower and small lower buds (“popcorn”) are the economic reason for these methods. They have little value as flower but real value as resin. Dry the material properly, store it airtight somewhere cool and dark, and break it up only when you process it.
Translator’s note: At the 80–90% humidity common in Thailand, stored trim can grow mould quickly if it is not fully dry or not sealed. Check stored material before each run, and discard any bag that smells musty or shows white or grey fuzz.
What to do: Inspect every bag of plant material before it goes into the can. Put aside anything with visible mould, and keep a record of which batches were rejected and why.
9. Thai legal status and the place of dry separation in a licensed operation
- The plant material. In Thailand, cannabis flower (ช่อดอกกัญชา) is a controlled herb under the Notification of the Ministry of Public Health Re: Controlled Herbs (Cannabis), B.E. 2568. It was issued under the Thai Traditional Medicine Protection Act B.E. 2542 and has been in force since 26 June 2025. Flower may be sold only with a PT 33 (ภ.ท.33) prescription, for at most 30 days’ supply, and advertising and online sale of flower are prohibited.
- The resin. The Category 5 status of extracts comes from the Narcotics Code and the Ministry of Public Health Notification on the specification of Category 5 narcotics, B.E. 2565 (2022). That notification took most cannabis plant parts off the narcotics list. It kept extracts in Category 5 unless they contain no more than 0.2% THC by weight and come from plants grown in Thailand.
- Licensing. The Ministerial Regulation on Cannabis or Hemp Extracts B.E. 2569 sets the rules for who may produce, import, export, sell or possess these extracts. It was published in the Royal Gazette on 26 March 2026. It has been in force since 26 April 2026. Licences for extracts above 0.2% THC go only to Thai juristic persons (registered companies and similar bodies) that are not “foreign” under the Foreign Business Act B.E. 2542, to state agencies and to the Thai Red Cross Society. Licences issued under the earlier extract rules remain valid until 31 December 2026. A separate Ministerial Regulation on Controlled Herbs (No. 2) B.E. 2569, in force since 30 April 2026, tightened the licence criteria for the flower trade.
- The open question. It is not clear whether mechanically separated resin (dry sift, trim-table kief or dry ice sift) legally counts as an “extract”. Confirm this with the Thai FDA or ONCB before any processing.
- Pending law. The draft Cannabis Control Act is not law yet. The Cabinet approved the draft on 22 September 2026 and sent it to the House of Representatives.
Producing, supplying or selling resin requires the relevant licence. Growing the flower legally does not make the resin legal.
In a licensed processing facility or a research setting, dry separation has clear advantages.
- No solvent. There is no solvent to recover, no testing for leftover solvent, and none of the fire and explosion risk that shapes the design of hydrocarbon (butane or propane) extraction facilities.
- No water. There is no drying step.
- Low equipment cost.
- Higher value from leftovers. It turns trim and popcorn buds into a more valuable product for licensed processors.
What it lacks is process control. Shaking a can by hand is not a repeatable process step, and choosing a screen by eye is not a specification. Scaling up means using rated monofilament screens, a fixed shaking time and temperature, and the safety controls from section 7, all written into an SOP (standard operating procedure, the written step-by-step method staff must follow).
What to do: Before any processing, write to the Thai FDA or ONCB with a description of your method and ask whether the product counts as an extract. Keep their written reply with your licence file.
10. Checklist
Before you start
- Licence status confirmed, and the “is it an extract?” question answered in writing.
- Ventilated work area, plus a CO₂ monitor if you do this regularly.
- Protective equipment as in section 7.2: cryogenic gloves, eye and face protection, long trousers, closed shoes.
- Plant material dry, stems removed, no visible mould.
- Screen size stated in microns, and the screen checked for damage.
- Tray warmed for 20 minutes.
During the run
- Gloves on before you touch the can.
- Eye protection on before you pick up the hammer.
- Mesh kept tight.
- No sealed containers, ever.
After the run
- Press promptly and keep resin covered between small batches.
- Rest it 30 minutes in the open, then store it airtight and dark for 3–4 days.
- If you used the water step, dry with a fan or dehumidifier, not in still room air, and send a sample for a microbial test.
- Keep the area ventilated until all the dry ice has turned to gas. Never leave dry ice in a closed room, a vehicle or a cold store.
Two questions for licensed processors and researchers
- Has anyone run dry ice separation and ice water separation on the same plant material and compared the results? The manual claims a large advantage for dry ice but gives no comparison. If you have done it, post the cultivar, the screen size in microns and the yield per 100 g of material in the replies below.
- Which regional landraces and Thai or Lao heritage genetics give clean dry-separated resin? Nobody has tested them systematically. A few real test-batch reports would be worth more than any amount of theory.
Related topics on this forum: ice water extraction and bubble hash, rosin and the Solventless and Hash board for other resin separation methods; drying without ruining the harvest, harvest, drying and curing in Thai heat and harvesting and drying in a hot, humid climate for preparing the plant material; reading a certificate of analysis for lab testing.
This article is technical processing information for readers acting legally where they live. In Thailand, cannabis extracts above 0.2% THC are Category 5 narcotics under the Narcotics Code and the Ministry of Public Health Category 5 notification B.E. 2565; the Ministerial Regulation on Cannabis or Hemp Extracts B.E. 2569 sets who may be licensed to handle them. Dry ice is a physical hazard that can cause serious injury and suffocation. The safety guidance above is a summary and does not replace a proper risk assessment. Nothing here is legal or medical advice.