In this chapter: how much weight is too much to lift by hand according to NIOSH and the law in each region, what to do about 25 to 40 kg bags and big bags, and which personal protective equipment is appropriate for each job in a wood pellet plant or feed mill.
The hazard that never makes the news
An explosion or an entrapment in a silo makes the news. An operator who injures their back after years of lifting bags doesn't show up anywhere. Yet it is an everyday hazard, and the regulations of Mexico, Argentina and the European Union address it with their own rules, as you will see in this chapter.
In a wood pellet plant or feed mill, manual handling happens when receiving bags of raw material, dumping premixes into the mixer, bagging and palletizing 25 to 40 kg bags, loading trucks, and handling big bags.
How much weight is too much
The NIOSH equation
In 1991, the U.S. National Institute for Occupational Safety and Health (NIOSH) revised its lifting equation, a method for evaluating manual lifting tasks and preventing low back pain1. It starts from a load constant of 23 kg: the maximum recommended weight for a lift under ideal conditions12.
Those ideal conditions almost never occur. The equation multiplies the 23 kg by six factors, and each one can only lower the limit2:
- the horizontal distance between the body and the load;
- the height from which it is lifted;
- the vertical distance the load travels;
- trunk twisting (asymmetry);
- the frequency of lifts and the duration of the task;
- the quality of the grip.
The result is the recommended weight limit for that specific task. Dividing the actual weight by that limit gives the lifting index, which NIOSH proposes for identifying hazardous tasks1.
The conclusion is straightforward: a 25 kg bag already exceeds the 23 kg constant, even under ideal conditions. A 40 kg bag lifted from the floor, with trunk twisting and many times per shift, is far above it.
Legal limits
- Mexico. NOM-036-1-STPS-2018, on ergonomic risk factors, sets the maximum mass a worker may lift or lower: 25 kg for men aged 18 to 45 and 20 kg for women aged 18 to 45, with lower values for those under 18 and over 45, in which case the limit is set by a medical evaluation. It prohibits pregnant women, and women up to 10 weeks after giving birth, from handling loads over 10 kg. For heavier loads, it requires mechanical aids or team lifting. It has been in force since January 2, 20203.
- Argentina. Resolución MTEySS 295/2003, in its Annex I on ergonomics, sets limit values for manual lifting in three tables, based on duration, frequency, height and horizontal distance, and calls for lowering them for shifts longer than 8 hours, trunk twisting, heat or poor grip, among other factors4. Resolución SRT 886/2015 approved the Ergonomics Protocol, which is mandatory and does not replace Annex I of Resolución 295/20035.
- European Union. Directive 90/269/EEC does not set a maximum weight. It requires the employer to avoid manual handling through organizational measures or mechanical equipment; when it cannot be avoided, to assess the task and organize the workstation to make it as safe as possible; and to train and inform workers6.
What to do about bags
The European Directive sets out the logical order, which applies in any country: first avoid manual lifting, then reduce it, and only at the end, train6. In a feed mill or pellet plant, that means:
- Mechanize where the most lifting happens, usually bagging and palletizing: conveyors, palletizers, lift tables or vacuum lifters.
- Switch the highest-volume raw materials to bulk or big bags.
- Reduce the bag weight. A 25 kg bag is much easier to handle than a 40 kg one, and in Mexico it is the legal maximum for a man aged 18 to 453.
- Work at the right height: pick up and set down the bag between knee and shoulder height. Loading openings on mixers and hoppers should be at that height.
- Avoid trunk twisting, rotate tasks and respect breaks.
- Train in lifting technique, knowing that training alone does not make up for a poorly designed workstation.
Big bags: the danger is underneath
A full big bag can weigh between 500 and 1,000 kg, depending on its contents7. The risk is not lifting it by hand, but being underneath or beside it when something fails.
In July 2022, in Victoria, Australia, a farmer was crushed to death between a big bag and a seed hopper. He was emptying the bag, which was hung by its loops directly from the forks of a telehandler, when the loops gave way7. After the incident, the Victorian safety authority recommended7:
- follow the bag manufacturer's instructions and never exceed its safe working load;
- inspect every bag before filling it and before each lift, especially the underside of the loops, and discard damaged ones;
- do not hang the bag directly from the forks of the forklift, whose edges can cut the loops: use a lifting attachment designed for the purpose;
- use all the loops on the bag;
- do not let anyone stand underneath a suspended bag, and use bags with bottom discharge or a discharge frame that lets people work at a distance.
ISO 21898:2024 sets the design, testing and marking requirements for big bags for non-dangerous goods, and gives guidance on their selection and safe use8. When you buy big bags, ask for them to be manufactured and marked to that standard.
Personal protective equipment: the last barrier
Personal protective equipment (PPE) does not eliminate the hazard. It only protects the person wearing it, and only if it is worn correctly. That is why it is the last line of defense, after eliminating the hazard or controlling it at the source. A dust mask does not replace dust collection on the mill.
What the regulations require
- United States. OSHA (29 CFR 1910.132) requires assessing the hazards of each job and documenting it in writing in a certification that states the workplace, the date and who performed it; selecting suitable PPE that fits each person properly; training on when to use it, how to put it on and take it off, its limitations and its care; and providing it at no cost to the worker, with some exceptions such as ordinary safety-toe footwear that can be worn off the job9.
- European Union. Two pieces of legislation go together: Regulation (EU) 2016/425 governs how PPE must be manufactured and placed on the market, and Directive 89/656/EEC sets the employer's obligations on its use, including assessing, before selecting it, whether the equipment meets the requirements10.
- Mexico. NOM-017-STPS-2024, Equipo de protección personal – Selección, uso y manejo en los centros de trabajo, was published in the Diario Oficial on March 28, 2025, came into force on September 28, 2025, and replaced NOM-017-STPS-200811.
- Argentina. Decreto 351/79 devotes its Title VI to the personal protection of workers (Chapter 19, articles 188 to 203), and Resolución SRT 299/2011 created the "Constancia de entrega de ropa de trabajo y elementos de protección personal," a form for each worker on which every issue is recorded12.
Which equipment for each job
The table is a general guide. The PPE for each job is defined by your plant's risk assessment.
| Job | Hearing | Respiratory | Eyes | Footwear | Hands |
|---|---|---|---|---|---|
| Receiving and unloading | Based on measurement | Yes, when dumping bags or trucks | Yes | Safety toe | Gloves for handling bags |
| Grinding | Yes | Yes | Yes | Safety toe | No gloves near moving parts |
| Premix and additive dosing | Based on measurement | Yes | Yes, depending on the product | Safety toe | Per the product's safety data sheet |
| Pelleting and cooling | Yes | Based on measurement | Yes | Safety toe | No gloves near moving parts |
| Bagging and palletizing | Based on measurement | Yes | Yes | Safety toe | Gloves for handling bags |
| Cleaning | Depending on the area | Yes | Yes | Safety toe | Depending on the task |
| Entry into silos and storage bins | Depending on the area | Based on gas monitoring (Chapter 7) | Yes | Safety toe | Depending on the task |
Hearing protection
Mills and pellet mills are the plant's main sources of noise. Limits, measurement and hearing protection are covered in Chapter 6.
Respiratory protection
There are two strong reasons to take the dust you breathe seriously:
- Wood dust. The International Agency for Research on Cancer (IARC) classified wood dust in Group 1, carcinogenic to humans, in its Monograph 62 of 1995: occupational exposure is associated with adenocarcinoma of the nasal cavity and paranasal sinuses13. In the European Union, the exposure limit for hardwood dust has been 2 mg/m³ since January 17, 202314.
- Flour and grain dust. Breathing flour dust can cause asthma, and so can some additives containing enzymes. The UK HSE sets a limit for flour dust of 10 mg/m³ over eight hours and 30 mg/m³ over 15 minutes, and requires exposure to be reduced as far below those values as is reasonably practicable15. A person who has already developed occupational asthma can react to very small amounts15.
For dust, use respirators with particulate filters: in Europe, class FFP2 or FFP3 under EN 149; in the United States, NIOSH-certified N95 respirators or higher19. The class is determined by the risk assessment. A dust respirator does not protect against carbon monoxide or against the lack of oxygen in a silo or pellet storage (Chapter 7).
When respirator use is required, OSHA (29 CFR 1910.134) requires a written program, a prior medical evaluation to determine whether the person can wear one, and a fit test before first use and at least once a year for tight-fitting respirators16.
Eye protection
Dust, flying particles and contact with premixes and additives justify safety glasses in almost the entire plant. For liquid or corrosive additives, the product's safety data sheet states what protection is needed.
Footwear
Safety-toe footwear throughout the plant: there are bags, pallets, heavy parts and forklifts. In Europe, ISO 20345 requires the toe cap of safety footwear to withstand an impact of at least 200 J17. The sole should be slip-resistant, because flour dust on the floor is slippery.
Gloves: useful, but not near anything that rotates
Gloves protect the hands when handling bags, strapping and parts with sharp edges. But near rotating parts they increase the risk of entanglement. The Northern Ireland safety authority (HSENI) is categorical: gloves are never acceptable near rotating machine parts18. The right approach is that nobody puts a hand near a moving part: fixed guards and lockout before any intervention (Chapter 4).
Chapter checklist
- Have we identified every job where bags are lifted by hand, and how many lifts each person makes per shift?
- Have we assessed those jobs with a recognized method (NIOSH, the table in Resolución 295/2003, NOM-036 or another)?
- Does the weight of our bags comply with our country's legal limit?
- Have we mechanized, or do we plan to mechanize, bagging and palletizing?
- Are the loading openings on mixers and hoppers at a reasonable height?
- Do we inspect big bags before each lift and use a suitable lifting attachment?
- Is standing underneath a suspended big bag prohibited?
- Do we have a written PPE assessment for each job?
- Do we record the PPE issued to each worker?
- Do respirator users have a medical evaluation and a fit test?
- Is wearing gloves near moving parts prohibited?
What to leave to a professional
The ergonomic assessment of each job, the measurement of airborne dust and the selection of PPE for each job must be done by an occupational health and safety professional, following your country's regulations. The medical evaluation for respirator use is done by a physician.
At Meelko, we design lines with the people who work on them in mind: the height of the loading openings, bagging and palletizing, and dust collection at the points where dust is generated are defined together with the plant's capacity. If you want to review your project or your plant, tell us about your project.
Chapter sources
- Waters T. R., Putz-Anderson V., Garg A. and Fine L. J. "Revised NIOSH equation for the design and evaluation of manual lifting tasks". Ergonomics 36(7):749-776, 1993. doi: 10.1080/00140139308967940. Copy at CDC: https://stacks.cdc.gov/view/cdc/205542 ↑
- NIOSH. Applications Manual for the Revised NIOSH Lifting Equation, Publication 94-110. https://www.cdc.gov/niosh/docs/94-110/ — CCOHS summary (Canada): https://www.ccohs.ca/oshanswers/ergonomics/niosh/assessing.html ↑
- Mexico. NOM-036-1-STPS-2018, Factores de riesgo ergonómico en el trabajo – Identificación, análisis, prevención y control. Parte 1: Manejo manual de cargas, signed on November 22, 2018, Table 1 and transitory provisions. https://sidof.segob.gob.mx/notas/docFuente/5544579 ↑
- Argentina. Resolución MTEySS 295/2003, Annex I, Especificaciones técnicas sobre ergonomía, section "Levantamiento manual de cargas". Copy: https://www.facet.unt.edu.ar/syso/wp-content/uploads/sites/36/2016/03/Res295-03-anexo1.pdf ↑
- Argentina. Resolución SRT 886/2015, Protocolo de Ergonomía. https://www.argentina.gob.ar/normativa/nacional/246272/texto ↑
- Council Directive 90/269/EEC of May 29, 1990, on the manual handling of loads where there is a risk particularly of back injury to workers. https://eur-lex.europa.eu/eli/dir/1990/269/oj ↑
- WorkSafe Victoria (Australia). Farmer killed while unloading bulka bags, safety alert, July 20, 2022. https://www.worksafe.vic.gov.au/safety-alerts/farmer-killed-while-unloading-bulka-bags ↑
- ISO 21898:2024, Packaging — Flexible intermediate bulk containers (FIBCs) for non-dangerous goods, 2nd edition, August 2024. https://www.iso.org/standard/83014.html ↑
- OSHA. 29 CFR 1910.132, Personal protective equipment – General requirements. https://www.law.cornell.edu/cfr/text/29/1910.132 ↑
- Regulation (EU) 2016/425 on personal protective equipment, and Directive 89/656/EEC on the use by workers of personal protective equipment. European Agency for Safety and Health at Work (EU-OSHA): https://osha.europa.eu/en/legislation/directives/4 and https://osha.europa.eu/en/legislation/directive/regulation-eu-2016425-personal-protective-equipment ↑
- Mexico. NOM-017-STPS-2024, Equipo de protección personal – Selección, uso y manejo en los centros de trabajo, DOF March 28, 2025. Official page: https://platiica.economia.gob.mx/normalizacion/nom-017-stps-2024/ ↑
- Argentina. Resolución SRT 299/2011 (Boletín Oficial, March 30, 2011), which creates the form Constancia de entrega de ropa de trabajo y elementos de protección personal (articles 2 and 3). https://www.argentina.gob.ar/normativa/nacional/norma-180669/texto — Decreto 351/79, Annex I, Title VI, Protección personal del trabajador, Chapter 19, Equipos y elementos de protección personal (articles 188 to 203). https://www.argentina.gob.ar/normativa/recurso/32030/dto351-1979-anexo1/htm ↑
- IARC. Monographs on the Evaluation of Carcinogenic Risks to Humans, Vol. 62: Wood Dust and Formaldehyde, 1995. https://publications.iarc.who.int/Book-And-Report-Series/Iarc-Monographs-On-The-Identification-Of-Carcinogenic-Hazards-To-Humans/Wood-Dust-And-Formaldehyde-1995 — Reviewed in Vol. 100C (2012). ↑
- Directive (EU) 2017/2398, amending Directive 2004/37/EC (carcinogens or mutagens), Annex III: hardwood dust, 3 mg/m³ until January 17, 2023, and 2 mg/m³ since then. European Parliament summary: https://oeil.europarl.europa.eu/oeil/en/procedure-document-summary/pdf?id=1517613 ↑
- Health and Safety Executive (HSE, United Kingdom). COSHH essentials for production and use of flour – FL0: Advice for managers. https://www.hse.gov.uk/pubns/guidance/fl0.pdf ↑
- OSHA. 29 CFR 1910.134, Respiratory protection. https://www.law.cornell.edu/cfr/text/29/1910.134 ↑
- ISO 20345:2021, Personal protective equipment — Safety footwear. Page: https://www.iso.org/standard/73222.html — Instituto Nacional de Seguridad y Salud en el Trabajo (INSST, Spain). Protección de pies y piernas: safety footwear protects against an impact of at least 200 J and a compression of at least 15 kN. https://www.insst.es/materias/equipos/epi/proteccion-de-pies-y-piernas ↑
- Health and Safety Executive for Northern Ireland (HSENI). Safety alert – Safe use of emery cloth. https://www.hseni.gov.uk/node/1822 ↑
- Health and Safety Executive (HSE, United Kingdom). All you need to know about disposable dust masks: disposable respirators are marked to EN 149:2001; classes FFP1, FFP2 and FFP3 reduce inhaled dust by factors of 4, 10 and 20, filter only dust, and are not suitable where there is a lack of oxygen or where gases or vapors are present. https://www.hse.gov.uk/agriculture/dustmasks.htm — United States. 42 CFR 84.170: N95 filters must have a minimum efficiency of 95%; the N series is only for environments free of oil aerosols. https://www.ecfr.gov/current/title-42/chapter-I/subchapter-G/part-84/subpart-K/section-84.170 ↑
