Dry guano (bird and bat droppings) and dried manure can carry fungal spores and other dust that harms the lungs. US health authorities treat clearing large amounts of bird or bat droppings as high-risk work, and they name the respirators to use for it. Two diseases make this especially important in Thailand and Southeast Asia. Histoplasmosis comes from droppings, and melioidosis comes from wet soil. This part explains both risks and how to choose a respirator. It also covers the controls a grower or fertiliser repacker should put into a written work procedure.
Part 1 covers how hot composting works, the time-temperature standards for killing pathogens, and which manures need composting.
This is Part 2. Part 1: Hot Composting Done Safely: Time-Temperature Standards and the Respiratory Hazard Nobody Warns You About
1. Histoplasmosis: the spore risk in dry droppings
Dried bird and bat droppings can contain Histoplasma capsulatum. This fungus causes histoplasmosis, an infection that starts in the lungs when you breathe in the spores. Disturbing a build-up of dry guano throws the spores into the air. It is a recognised workplace hazard, and published guidance exists on how to control it.
The US Centers for Disease Control and Prevention (CDC) covers this through its workplace-safety institute, NIOSH (National Institute for Occupational Safety and Health). Their joint web page is Personal Protective Equipment | Histoplasmosis, dated 18 January 2024. It lists two high-risk activities:
- cleaning up large build-ups of bird or bat droppings;
- entering caves or tunnels that contain bat droppings.
Histoplasmosis is endemic in Thailand, meaning the disease is regularly present here. Thailand is one of the Asian countries where endemic histoplasmosis is documented. In 2022, Thai news media reported a group of cases in Nakhon Si Thammarat, first described by a respiratory physician at Vichaiyut Hospital. Seven of ten people in a hiking group fell ill after briefly entering a hollow tree where bats roosted. They did not need to handle any droppings. Breathing the air inside the hollow was enough.
Much of the guano in this region is collected from caves. Under the CDC guidance, entering caves or tunnels with bat droppings is high-risk work. Anyone who collects guano directly from caves or roosts should treat the job as high-risk.
What to do: List every task on your farm or in your store that disturbs dry droppings. Mark cave or roost collection and bulk handling as high-risk.
2. What the CDC recommends for high-risk work
For the high-risk activities above, the CDC/NIOSH page recommends one of two options:
- A powered air-purifying respirator (PAPR) with an approved filter. A PAPR uses a battery-powered fan to push air through a filter into a hood or mask. It can be loose-fitting (a hood or loose face cover) or tight-fitting (a sealed mask). According to the page, approved filters for both types are HE, PAPR100-N and PAPR100-P.
- A full-face respirator with 100-series filters. This mask covers the eyes, nose and mouth, and you breathe through the filters. 100-series filters are the highest filter class in the US system and are marked N100, R100 or P100. They have a filter efficiency of 99.97%.
The page treats disposable filtering masks such as the N95 as a last resort. It says they “only have an assigned protection factor of 10”. It also says they give only 20% of the protection of PAPRs (protection factor 25–50) and full-face air-purifying respirators (protection factor 50). Use them only if a PAPR or a full-face respirator with 100-series filters is not available.
For medium-risk work, such as disturbing soil outdoors or farming, the page says to consider half-face respirators. These include filtering masks such as the N95.
What to do: For each high-risk task on your list, write down which of the two recommended respirators the worker will use.
3. Choosing a respirator: N95, PAPR and the protection factor
The assigned protection factor (APF) shows how much a correctly worn respirator cuts what you breathe in. With APF 10, you breathe in about one-tenth of the dust in the surrounding air. With APF 50, you breathe in about one-fiftieth. The higher the number, the better the protection.
The main types are:
- N95 or FFP2 mask. A disposable mask that filters the air as you breathe through it. FFP2 is the European class, usually treated as equivalent to the US N95. It only works if it seals well against your face.
- Half-face respirator. A reusable rubber or silicone mask over the nose and mouth, with replaceable filters.
- Full-face respirator. It also covers the eyes and seals around the whole face. Used with 100-series filters, it is one of the two CDC options for high-risk work.
- PAPR. A fan pushes filtered air into a hood or mask. Breathing feels easier because you do not have to pull air through the filter yourself.
The CDC’s “25–50” range for PAPRs is a simplification. The US Occupational Safety and Health Administration (OSHA) gives exact figures in its respiratory protection standard (29 CFR 1910.134, Table 1):
| Respirator type | APF set by OSHA |
|---|---|
| PAPR with a loose-fitting face cover | 25 |
| PAPR with a half mask | 50 |
| PAPR with a tight-fitting full-face mask | 1,000 |
| PAPR with a helmet or hood | 25, unless the manufacturer has test evidence supporting 1,000 |
The working rule for bulk dry guano is APF 25 or higher. The background document is NIOSH’s Histoplasmosis: Protecting Workers at Risk, revised edition (DHHS (NIOSH) Publication No. 2005-109, December 2004).
How to match the respirator to the job:
| Task | Minimum protection |
|---|---|
| Collecting guano from caves or roosts, cleaning large build-ups of droppings, decanting bulk dry guano | APF 25 or higher: a PAPR with an approved filter, or a full-face respirator with 100-series filters. N95 only if neither is available |
| Opening and using bags of dry processed guano | APF 25 or higher, plus dampening the material and opening gently |
| Large volumes of dried poultry manure | At minimum a well-fitted N95/FFP2; better, the same controls as for guano (section 4) |
| Opening and using perlite | At minimum a well-fitted N95/FFP2, plus a little water in the bag on opening |
| Disturbing soil outdoors, general farm work | Consider a half-face respirator, including filtering masks such as the N95 |
| Wet soil, compost or manure | Rubber gloves and boots, with cuts covered (section 6) |
A tight-fitting mask protects you only when it seals against the skin. Facial hair under the seal lets air leak in around the filter. A “well-fitted” mask is one that has no gaps when you breathe in.
Translator’s note: N95-type masks are easy to find in Thailand because many people buy them for the PM2.5 haze season. PAPRs and full-face respirators are usually sold through industrial safety-equipment suppliers. A full-face respirator usually costs less than a PAPR, which makes it the practical first choice for a small operation. If you cannot get either, cut the risk in other ways. Dampen the material, work outdoors and upwind, handle smaller amounts at a time, and only use an N95 as the CDC’s last resort. Charge a PAPR’s battery before each job, and keep a spare in case of a power cut.
What to do: Buy a respirator that matches the riskiest task on your list. Check the seal on every worker before each job.
4. A written procedure for repacking bulk guano
Many fertiliser distributors in this region repack bulk guano, and a basic dust mask is not enough for the job. Pouring dry guano in bulk keeps dust hanging in the air of a closed room. Write the controls into a standard operating procedure (SOP), the written step-by-step instructions every worker follows:
- Respiratory protection at APF 25 or higher for everyone who pours or repacks, not just an N95. That means a PAPR, or a full-face respirator with 100-series filters. Purpose: the people closest to the dust get the strongest protection.
- Dampen the material lightly before you disturb it. Purpose: less dust gets into the air in the first place.
- Use local exhaust ventilation, meaning extraction that pulls air away at the point where dust is made, or do the work outdoors and upwind. Purpose: dust is carried away from the worker.
- Wear disposable coveralls and gloves, and take them off before leaving the work area. Purpose: dust is not carried into the office, the vehicle or the home.
- Keep other people out of the area while the work is going on. Purpose: you can catch histoplasmosis just by breathing the air nearby, without touching the material.
Translator’s note: Coveralls and a full-face mask are hard to wear at 30–35 °C. Schedule the work for the cooler early morning, and plan rest breaks outside the dust area. Close the area to everyone not taking part, including other staff and customers.
What to do: Turn the five controls above into a one-page SOP, and train every person who handles bulk guano on it before their next shift.
5. Perlite and dried manure dust
Two other dusts belong in the same SOP:
- Perlite dust is generally classed as a nuisance dust. Some products, however, can contain traces of crystalline silica, a mineral dust that is harmful to breathe. Check the safety data sheet (SDS), the supplier’s document that lists a product’s hazards and how to handle it. When you open a bag, spray a little water inside it. Wear at minimum a well-fitted N95/FFP2.
- Dried poultry manure and similar dried manure products give off dust that contains microbes and endotoxins. Endotoxins are fragments of bacterial cell walls that irritate the lungs when breathed in. Wear at minimum a well-fitted N95/FFP2. For large volumes, it is better to use the same controls as for guano.
What to do: Ask your supplier for the SDS of every perlite product you use and keep it on file. Put a water spray bottle next to the perlite and manure store.
6. Melioidosis: the wet-soil risk in Isan and Laos
Burkholderia pseudomallei is the bacterium that causes melioidosis. It lives in soil and surface water. It is a major risk in north-eastern Thailand (Isan) and neighbouring Laos, and cases peak in the rainy season. It enters the body mainly through cuts and skin wounds. People can also catch it by breathing in or swallowing contaminated soil or water.
Diabetes is the most important risk factor for severe melioidosis.
When you handle wet soil, compost or manure:
- wear rubber gloves and boots;
- cover any cuts;
- do not work barefoot or with your feet soaking in water;
- if you have diabetes, follow all of the above strictly.
If you get a fever after contact with soil, see a doctor and tell them about the exposure. That gives the doctor the information needed to consider melioidosis.
Translator’s note: The rainy season is also the main season for mixing soil and turning compost on many farms. Keep gloves and boots next to the compost pile so nobody works without them “just for a minute”. Ask staff whether they have diabetes, privately and with care, so the rule can be explained to them clearly.
What to do: Put rubber gloves, boots and waterproof plasters at every place where wet soil or compost is handled.
7. A written protection rule for your farm or store
Put together, the rule that matches protection to material is:
- Bulk dry guano: APF 25 or higher (a PAPR, or a full-face respirator with 100-series filters).
- Dried manure and perlite: at minimum a well-fitted N95/FFP2, plus water in the perlite bag on opening.
- Wet soil and compost: gloves and boots, with cuts covered.
What to do: Print this rule and post it at the entrance to every area where guano, manure, perlite or compost is stored or handled.
8. What is confirmed and what is not
Confirmed:
- The CDC/NIOSH respirator recommendations for bird and bat droppings, and the OSHA protection factors in section 3.
- That histoplasmosis is endemic in Thailand.
- That melioidosis is concentrated in north-eastern Thailand, and that diabetes is its main risk factor.
A precaution, not a measured result: the perlite advice (N95/FFP2 plus dampening) is a minimum. Silica content varies from product to product, so check the SDS.
If you handle bulk guano or manure, share your SOP’s respiratory protection below this topic. Say how it compares with the CDC/NIOSH guidance above, so other growers and repackers can check their own procedures against it.
References
- CDC/NIOSH. Personal Protective Equipment | Histoplasmosis (2024). https://www.cdc.gov/niosh/histoplasmosis/prevention/personal-protective-equipment.html
- NIOSH. Histoplasmosis: Protecting Workers at Risk, revised edition. DHHS (NIOSH) Publication No. 2005-109, 2004. https://stacks.cdc.gov/view/cdc/209861
- OSHA. 29 CFR 1910.134, Table 1: Assigned Protection Factors. https://www.osha.gov/laws-regs/regulations/standardnumber/1910/1910.134
This article is technical information on horticulture and workplace safety for readers who operate legally where they live. It is not medical advice. If you have had a significant exposure to bird or bat droppings and develop breathing symptoms, see a doctor and tell them about the exposure. Every country regulates cannabis cultivation differently. In Thailand, cannabis flower is a controlled herb under Ministry of Public Health rules, and its sale, processing, research and export need a licence. Check your local law before you grow. Nothing here is legal advice.