1.1 What hazardous energy is, and who gets hurt

1 The word that carries the whole standard: unexpected

29 CFR 1910.147(a)(1)(i) says the standard covers the servicing and maintenance of machines and equipment "in which the unexpected energization or start up of the machines or equipment, or release of stored energy could cause injury to employees," and that it establishes minimum performance requirements for the control of such hazardous energy.

Read that again and notice what it does not say. It does not say electricity. It does not say high voltage. It does not say big machines. It says unexpected, and it says energy — any energy, in any amount that can hurt someone. A 12-inch length of compressed air line at 90 psi has enough energy to drive a fitting through a hand. A pneumatic cylinder holding a die up has enough stored energy to close it. A conveyor motor that draws four amps has more than enough torque to pull an arm into a nip point.

The whole apparatus of lockout/tagout — the written procedure, the personal lock, the verification step, the annual inspection — exists to convert "unexpected" into "impossible." Everything you learn in this course is a mechanism for taking one specific machine, at one specific moment, out of the category of things that can surprise you.

2 A standard OSHA cites constantly

OSHA publishes a list of the ten standards it cites most often after workplace inspections. In fiscal year 2025, the control of hazardous energy — 1910.147 — was number four across all industries, behind only construction fall protection, hazard communication, and construction ladders. It has sat in the top five for years.

That ranking tells you something useful about how this standard fails in practice. Nobody gets cited for not owning padlocks. The citations cluster around paperwork that does not match the machine, procedures that were written once and never walked, training that was a video in 2019, and periodic inspections that nobody has done. The physical act of hanging a lock is the easy part; the standard is mostly about the system that makes the lock mean something.

3 How people actually get hurt

The failure modes repeat themselves across industries with depressing regularity. None of them are exotic. Each one maps to a specific requirement you will meet later in this course.

Read down the middle column. Not one of those is a hardware problem. They are all failures of knowledge, sequence or communication — which is exactly what a program made of procedures, training and inspections is designed to prevent, as 1910.147(c)(1) puts it.

4 Servicing is not the same as running the machine

A distinction runs through the entire standard and it trips people up constantly: 1910.147 is about servicing and maintenance, not about production. 1910.147(a)(2)(i) states that the standard applies to the control of energy during servicing and/or maintenance of machines and equipment, and (a)(2)(ii) says plainly that normal production operations are not covered — those belong to subpart O, the machine guarding standards.

The definition of "servicing and/or maintenance" at 1910.147(b) is broader than most crews assume. It covers constructing, installing, setting up, adjusting, inspecting, modifying, and maintaining or servicing machines — and it explicitly names lubrication, cleaning, unjamming, and making adjustments or tool changes, wherever the employee may be exposed to unexpected energization, startup, or release of hazardous energy.

Unjamming is on that list, and it is the single most common place where a plant tells itself a story. Clearing a jam feels like production work — it happens twenty times a shift, it takes forty seconds, the operator does it without thinking. Under the definition above it is servicing, and if the operator has to reach past a guard into the point of operation to do it, Chapter 2 of this part will show you exactly why the standard follows them in there.

5 What a lock actually does

A lockout device, defined at 1910.147(b), is "a device that utilizes a positive means such as a lock, either key or combination type, to hold an energy isolating device in a safe position and prevent the energizing of a machine or equipment." Blank flanges and bolted slip blinds are included in that definition, which is a useful reminder that a lock is not always a padlock.

Three ideas are packed into that sentence, and they are worth separating out:

1. 1
   Positive means. The device physically holds the isolating device. It does not request, warn or remind. If it can be defeated by a decision, it is not a lockout device.
2. 2
   On an energy isolating device. The lock goes on the thing that breaks the energy path — the disconnect, the valve, the block — never on a control that merely tells the machine to stop.
3. 3
   Prevents energizing. The test is not whether the machine is currently off. It is whether it can be turned on while the lock is there.

A tagout device, by contrast, is defined in the same paragraph as "a prominent warning device" — it indicates that the isolating device may not be operated. It restrains nobody. 1910.147(c)(7)(ii)(A) says so in the training requirements themselves: tags are essentially warning devices and do not provide the physical restraint that a lock provides. Part 4, Chapter 4 covers the narrow circumstances in which a tag is nevertheless the correct answer.

6 Three roles, and why yours matters

1910.147(b) defines two categories of people, and (c)(7)(i)(C) adds a third. An authorized employee is the person who locks out or tags out a machine in order to service it. An affected employee is someone whose job requires operating or using that machine, or working in the area where the servicing is happening. Everyone else who may be in an area where energy control procedures are used gets instruction too — mainly so that they never try to restart or reenergize something that is locked out.

The categories are not job titles; they follow the task. The same definition notes that an affected employee becomes an authorized employee when their duties include performing covered servicing. An operator who clears their own jams under a lockout procedure is an authorized employee for that task and an affected employee the rest of the shift. Chapter 3 of this part unpacks the vocabulary in detail, because getting these labels right is what determines who has to be trained on what.

One last thing before you move on. 1910.147(c)(8) says lockout or tagout shall be performed only by the authorized employees who are performing the servicing or maintenance. Not by the supervisor on their behalf. Not by the electrician who happened to be walking past. The person exposed to the hazard is the person who controls the energy — that principle sits underneath almost every rule in the rest of this course.