In this chapter: where the machines in a wood pellet plant or feed mill catch, cut and strike, what guards exist, why pressing the stop button is not enough before you put your hands in, and what a new machine should come with from the factory.
Hands go where the problem is
In a wood pellet plant or feed mill, almost everything rotates: rotors, shafts, screw conveyors, belts, pulleys, chains, paddles. While the machine runs with its guards in place, the hazard is under control. Serious accidents almost always happen at another moment: when someone removes a cover to clear a jam, cleans a discharge opening, changes a screen or checks why a machine is making a strange noise.
The statistics confirm it. In the United States, the Bureau of Labor Statistics (BLS) recorded 6,200 work-related amputations with days away from work in 2018. 58% (3,580 cases) involved some type of machinery, and workers needed a median of 31 days to return to work1. An amputation also cannot be undone: it is a lifelong disability.
That is why OSHA has kept a national inspection program focused on amputations in manufacturing for years. Its 2025 version explains that workers who perform servicing and maintenance are often injured when machine guarding is missing or when energy control procedures are not applied. That version added to the list of inspected industries the code for "other wood product manufacturing," which is where the official index of industry codes places wood pellet manufacturing2.
Where machines catch, cut and strike
Every machine has its hazard points. These are the ones you most need to know in a plant like yours:
- Hammer mill. The rotor turns at high speed and keeps turning by inertia after the power is cut. Opening the inspection door before it comes to a complete stop is very dangerous. In addition, a metal object that enters with the material can be thrown out.
- Mixer. The internal ribbons or paddles can catch a hand or an arm through the loading opening, the inspection cover or the discharge screw.
- Pellet mill. The most dangerous point is the contact between the rollers and the die, where the material is compressed with enormous force. There is also a hazard at the feeder and the conditioner, the cutting knives, the drive, and the hot surfaces and steam.
- Screw conveyors. A cover left off or an open opening puts the screw within reach of a foot or a hand, and the screw pulls inward.
- Bucket elevators and belt conveyors. The head and boot pulleys, the inspection door at the elevator boot and the point where the belt enters the drum draw in clothing, gloves and fingers.
- Drives. Belts, pulleys, chains, couplings and projecting shafts. A smooth rotating shaft can catch a sleeve or hair.
Two hazards repeat in almost all of them: the part that keeps moving after shutdown and stored energy, such as material held in a hopper, compressed air in a gate or steam in a pipe.
A case: the cover without an interlock
In May 2014, in Kentucky (U.S.), a 21-year-old foreman died at a concrete mixing plant. He was cleaning the plant with the mixer running. As he was leaving, he stepped on one of the covers over the mixing auger section. The cover had broken hinges and its interlocks were missing, which he did not know. He fell with the cover into the running auger. When a coworker hit the emergency stop, it was too late3.
It was not a feed mill, but the machine is very similar to the ones you have. The NIOSH report recommended written maintenance procedures, inspection and immediate repair of damaged hinges and interlocks, training to recognize the hazard and, for manufacturers, that covers cannot be opened while the equipment is running3. The lesson: a broken or bypassed guard is worse than none, because everyone trusts that it is there.
Guards: from the safest to the least safe
The first rule is that no one's body reaches a moving part. There are several solutions for this, and they are not all equal:
- Fixed guards. Covers, sheets or mesh that can only be removed with a tool. They are the preferred solution for parts that don't need frequent access, such as drives, belts and couplings.
- Interlocking movable guards. Doors or covers that open for access, connected to a device that prevents the machine from starting while they are open and stops it if they are opened. When the hazardous part keeps turning by inertia, like a mill rotor, the door must also have a guard locking device that keeps it closed until the movement stops4.
- Protective devices. Light curtains, two-hand controls or other sensors that stop the machine when they detect a person in the danger zone.
- Signs, procedures and personal protective equipment. They are necessary, but they come last: they do not replace a physical guard.
In the United States, OSHA's general machine standard (29 CFR 1910.212) requires protecting the operator and other employees in the area from points of operation, ingoing nip points, rotating parts and flying chips and sparks. Guards must be affixed to the machine where possible and must not create a new hazard5.
The emergency stop is not a lockout
With few exceptions, machines must have an emergency stop that is easy to identify and reach. The European Machinery Regulation requires it to stop the hazardous process as quickly as possible, to stay latched until someone deliberately releases it, and that releasing it must not restart the machine4.
But the emergency stop is for halting an accident that is happening. It is not for working inside the machine: another person can release it and start the machine from the control room. To intervene, you need lockout, which we cover next.
Never bypass an interlock
Defeating an interlock "so the machine doesn't stop every time the cover is opened" leaves the machine unprotected while everyone believes it is protected. If an interlock gets in the way, there is a problem that must be solved with the manufacturer, not with a wire or a piece of tape. Mexico's NOM-004 requires workers to report safety devices that are damaged, out of service or blocked6. Make it a written rule in your plant.
Lockout/tagout: before you put your hands in
Lockout/tagout (LOTO; in Spain it is called consignación) means isolating the machine from all its energy sources, securing those isolation points with a personal lock and a tag, releasing stored energy and verifying that the machine cannot move before starting work.
What OSHA requires (29 CFR 1910.147)
OSHA's standard on the control of hazardous energy applies to the servicing and maintenance of machines when an unexpected startup or the release of stored energy could injure someone7. Its main points are:
- A written program, with procedures for each piece of equipment, training and inspection of the procedure at least once a year.
- Lock before tag. If the energy isolating device can accept a lock, a lock is used. Locks and tags are used only for lockout, are standardized and identify the person who applied them.
- An orderly sequence: prepare, shut down the machine, isolate each source, apply locks and tags, release stored energy and verify that the machine does not start before beginning work.
- Controlled removal: inspect the work area, notify personnel and each lock is removed by the person who applied it.
- Special rules for group lockout (each member applies their own lock), shift changes and contractors.
Minor production tasks that are routine and integral to the process are excluded if other effective protection is in place. But as soon as someone must remove or bypass a guard, or place any part of their body in the danger zone, lockout is mandatory7.
Which energies must be locked out
It is not only electricity. Review, machine by machine, electrical energy; mechanical energy from rotors that keep turning and tensioned belts; pneumatic energy from gates and filter cleaning; hydraulic energy; thermal energy from steam and hot surfaces; and gravity: material held in hoppers and bucket elevators that can fall, and gates that can close under their own weight.
A concrete example: before changing a pellet mill die or a hammer mill screen, you must lock out the energy of the machine and of the equipment that feeds it, wait until everything has stopped and verify that nothing can move. How each change is done is set out in your equipment manufacturer's manual and is not a subject of this book.
The equivalent in other countries
- Mexico. NOM-004-STPS-1999 requires energy lockout before and during maintenance: notify those involved, identify the points to be immobilized, lock out, apply warning tags and locks, verify the lockout and give notice when removing it. The person who applied the tags is the one who removes them6.
- Argentina. Decreto 351/79 requires electrical installations to be isolated and secured before work and makes clear that locking the switch is not enough on its own8. The Superintendencia de Riesgos del Trabajo guide on machines adds that cleaning and maintenance are done only by authorized personnel and with the equipment de-energized9. We cover this in Chapter 5.
- European Union. In Spain, the INSST's NTP 1117, Consignación de máquinas (2018), is a practical guide for putting procedures together10.
What a new machine should come with
Much of safety is decided at the time of purchase. A poorly designed machine forces you to improvise guards for the rest of its service life.
European Union: the Machinery Regulation
Regulation (EU) 2023/1230 replaces Machinery Directive 2006/42/EC and applies to machinery placed on the market from January 20, 202711. It requires the manufacturer to meet the essential health and safety requirements in Annex III, prepare the technical documentation, issue the EU declaration of conformity and affix the CE marking4. Among the Annex III requirements that matter most in your plant are: protected moving parts (section 1.3.7); drives with fixed or interlocking guards (1.3.8.1); interlocking guards and, if the part keeps moving, locked until it stops (1.4.2.2); emergency stop (1.2.4.3); maintenance with the machine stopped and maintenance points outside danger zones (1.6.1); and devices to isolate each energy source, identified and lockable, with a means to dissipate residual energy (1.6.3)4.
Mexico and the United States
NOM-004-STPS-1999 is addressed to the employer, but it defines what the machine must have in order to be used: sturdy fixed guards that do not create a hazard themselves, an easily activated emergency stop, devices so that a power failure does not create hazardous conditions, and a control protected against accidental activation. It also requires a risk study for each machine and a specific safety program for its operation and maintenance6.
In the United States, OSHA requires all new, replaced or overhauled equipment since January 2, 1990 to be able to accept a lockout device7.
What to ask the supplier
When you buy a machine, ask in writing for the standards it complies with, which guards come as standard, whether the inspection doors have interlocks (and guard locking until standstill on machines with inertia), where the isolation points for each energy source are and whether they accept a lock, and the manual in your language.
Chapter checklist
- Have we identified the catching, cutting and striking points on every machine?
- Do all drives (belts, chains, couplings, shafts) have fixed guards in place?
- Do the inspection doors on mills, mixers and pellet mills have interlocks? Do they work?
- Do we check periodically that no interlock is bypassed or broken?
- Are the emergency stops visible, within reach and tested?
- Is there a written lockout procedure for each machine that covers all its energy sources?
- Does every person who intervenes have their own lock and tag?
- Do contractors know and follow our lockout procedure?
- Is the lockout procedure reviewed at least once a year?
- When we buy a machine, do we ask in writing for its guards and lockout points?
What to leave to a professional
The risk study for each machine, the design of custom guards and the writing of lockout procedures must be done by a safety professional, together with the maintenance staff who know the equipment. Any modification to guards or interlocks should be discussed with the manufacturer: a poorly adapted guard can create a new hazard.
At Meelko, we plan guards and lockout points together with the design of the line, so maintenance can be done with the machine stopped and isolated. If you want to review your project or the machines in your plant, tell us about your project.
Chapter sources
- U.S. Bureau of Labor Statistics. Machinery involved in 58 percent of work-related amputations in 2018, The Economics Daily, 2020. https://www.bls.gov/opub/ted/2020/machinery-involved-in-58-percent-of-work-related-amputations-in-2018.htm ↑
- OSHA. Directive CPL 03-00-027, National Emphasis Program on Amputations in Manufacturing Industries, signed on May 29, 2025, effective June 27, 2025, for five years; section IX (background) and Appendix B, where NAICS code 321999 (All other miscellaneous wood product manufacturing) is marked with an asterisk, that is, as new compared with the 2019 program. https://www.osha.gov/sites/default/files/enforcement/directives/CPL-03-00-027.pdf — The entry "Wood pellets manufacturing" is listed under code 321999 in the U.S. Census Bureau's 2022 NAICS index: https://www.census.gov/naics/2022NAICS/2022_NAICS_Index_File.xlsx ↑
- NIOSH, Kentucky FACE program. Report 14KY022, Foreman Falls into Running Auger after Stepping on Door Panel with Broken Door Interlocks, February 11, 2015. https://stacks.cdc.gov/view/cdc/165054 ↑
- Regulation (EU) 2023/1230 of the European Parliament and of the Council of June 14, 2023, on machinery. OJ L 165, June 29, 2023. Article 10 and Annex III, sections 1.2.4.3, 1.3.7, 1.3.8.1, 1.4.2.2, 1.6.1 and 1.6.3. https://www.boe.es/doue/2023/165/L00001-00102.pdf ↑
- OSHA. 29 CFR 1910.212, General requirements for all machines. https://www.law.cornell.edu/cfr/text/29/1910.212 ↑
- Mexico. NOM-004-STPS-1999, Sistemas de protección y dispositivos de seguridad en la maquinaria y equipo que se utilice en los centros de trabajo, DOF May 31, 1999. Sections 5.2, 6.3, 7.2.2, 8.1, 8.2 and Appendix A. https://www.gob.mx/cms/uploads/attachment/file/680125/NOM-004-STPS-1999.pdf ↑
- OSHA. 29 CFR 1910.147, The control of hazardous energy (lockout/tagout). Paragraphs (a), (c)(2), (c)(5), (c)(6), (d), (e) and (f). https://www.law.cornell.edu/cfr/text/29/1910.147 ↑
- Argentina. Decreto 351/79, Annex VI (electrical installations), points 1.1.3, 1.1.4 and 2.4.2. https://www.argentina.gob.ar/normativa/recurso/32030/dto351-1979-anexo6/htm ↑
- Superintendencia de Riesgos del Trabajo (Argentina). Guía técnica de prevención 03: Protecciones en máquinas, equipos y herramientas, 2019. Refers to Decreto 351/79, Annex I, Chapter 15. https://www.argentina.gob.ar/sites/default/files/03_guia_protecciones_en_maquinas_equipos_y_herramientas_ok.pdf ↑
- INSST (Spain). NTP 1117, Consignación de máquinas, 2018. https://www.insst.es/documents/94886/566858/ntp_1117w.pdf/8ecd51a7-09bc-41b8-adb7-aec5349285bc ↑
- EU-OSHA, Regulation (EU) 2023/1230 on machinery (applicable from January 20, 2027). https://osha.europa.eu/es/legislation/directive/regulation-20231230eu-machinery — The date in the original text (January 14, 2027) was corrected by the corrigendum published in OJ L 169, July 4, 2023: https://eur-lex.europa.eu/eli/reg/2023/1230/corrigendum/2023-07-04/oj/spa ↑
