ANSI B11.TR3: Risk Assessment and Risk Reduction

The ANSI B11.TR3 risk assessment is a structured, team-based method for finding hazards on a machine tool, rating each one by how bad the harm could be and how likely it is, and then reducing the risk through a set order of controls until what remains is acceptable. It was published as B11.TR3-2000 and reaffirmed in 2015 as a voluntary technical report, not a regulation.¹ The voluntary label is misleading in practice, though, because OSHA references the B11 series when enforcing its machine guarding rule at 29 CFR 1910.212.²

TR3 sits alongside the numbered B11 standards as the “how” behind ANSI B11.0’s general safety principles.³ Where B11.0 says risk must be reduced to an acceptable level, TR3 shows a team how to get there.

What TR3 Covers

The report applies to machine tools within the B11 series, meaning power-driven equipment used to shape or form materials in industrial settings. Its guidance runs across the full lifecycle: design, construction, installation, operation, maintenance, and decommissioning.⁴ New machines, modified machines, and older equipment installed before the report existed can all be assessed with the same method.

Machine builders use TR3 to build safety in at the design stage. Employers use it to keep working conditions safe and to show due diligence. System integrators use it too, since combining machines on a line often creates hazards that neither piece of equipment had alone.¹

Building the Assessment Team

TR3 is designed to be run by a team, not a single engineer. The recommended mix is machine operators, maintenance personnel, and engineers who know the design.⁵ Operators know the near-misses and workarounds that never make it into a report. Maintenance workers see failure modes that only appear during repairs. Engineers can judge whether a proposed control is feasible. Drop any one of those perspectives and the assessment tends to develop blind spots.

Information to Gather Before Rating Risk

Before anyone rates a hazard, the team collects the machine’s physical limits: dimensions, speed, force, stroke, and the materials it processes. Every intended use gets defined, along with foreseeable misuse. A press built for flat sheet metal might foreseeably see stock that runs slightly too thick, and the assessment has to reflect that.

Every task that puts a person near the machine gets listed: routine operation, setup, cleaning, tool changes, jam clearing, troubleshooting. For each task, the team identifies specific hazards, from mechanical pinch points and shearing zones to electrical, thermal, noise, and ejection hazards. Manufacturer specifications give the technical baseline. Internal injury logs flag recurring trouble with similar equipment. One caution the method emphasizes: an absence of prior injuries is not evidence of low risk.⁶ A machine that has never hurt anyone can still carry serious uncontrolled hazards.

Rating Severity and Probability

Each hazard gets a risk level from two inputs: how severe the potential harm could be, and how likely that harm is to occur. TR3 uses four severity categories and four probability categories, which meet on a matrix to produce a rating of High, Medium, Low, or Negligible.⁶

The severity categories are:

Catastrophic: fatality or permanently disabling injury.
Serious: severe injury requiring significant medical treatment.
Moderate: injury requiring more than first aid.
Minor: injury treatable with first aid or less.

The probability categories are:

Very likely: harm is expected to occur during the task.
Likely: harm will probably occur at some point.
Unlikely: harm is possible but not expected.
Remote: harm is conceivable but highly improbable.

A catastrophic or serious hazard rated very likely or likely produces a High risk level. Moderate severity with very likely exposure also rates as High. At the other end, minor severity with unlikely or remote probability lands at Negligible. Combinations like catastrophic severity with unlikely probability produce Medium, while serious severity with remote probability produces Low.⁶

Probability accounts for more than raw exposure count. The team weighs frequency of exposure, duration of each exposure, the technical possibility of avoiding the hazard, and human factors like fatigue or time pressure. The point is a realistic picture, not a best-case one, which is why teams that include hands-on operators tend to produce more accurate ratings than teams working only from engineering documents.

Is the Risk Acceptable?

After each rating, the team decides whether the current level is acceptable or needs reduction. ANSI B11.0 defines acceptable risk as risk reduced to a level that can be tolerated given current technology, cost, and societal expectations.³ High-rated hazards clearly need action, and Medium ratings typically do as well. Low or Negligible may be acceptable, but the team should record the reasoning either way.

Applying Controls in Order

When a risk is unacceptable, TR3 requires controls to be applied in a set order of effectiveness. The point of the hierarchy is to give priority to the most reliable methods, not the cheapest or fastest.⁶

Eliminate the hazard by design. Redesign the machine or process so the danger no longer exists. Engineering a pinch point out of the machine beats every other option.
Engineering controls. Install physical safeguards such as barrier guards, interlocked enclosures, or light curtains that keep people out of the hazard zone. These don’t depend on anyone remembering a rule.
Administrative controls. Warning signs, safe-work procedures, lockout/tagout, and operator training. These rely on human behavior, which makes them less reliable than physical barriers.
Personal protective equipment. Safety glasses, cut-resistant gloves, hearing protection. PPE is last because it does nothing to remove or block the hazard itself.

Each level must be exhausted or documented as infeasible before moving to the next. A facility that jumps straight to training and PPE without showing why engineering controls won’t work has not followed the method. Most real machine hazards end up covered by a combination of controls from more than one level.

Re-Assessing After Each Control

Risk reduction under TR3 is not a single pass. After a control is applied, the team re-estimates the risk. Did the control actually bring the hazard to an acceptable level? Did it introduce any new hazards? A guard that removes a pinch point but creates a sharp edge hasn’t solved the problem, only changed it. The loop continues until every identified hazard sits at an acceptable level.⁷ Sometimes one measure is enough. Sometimes it takes several rounds.

What to Document

Every step must be recorded. The file should include a description of the machine and its intended limits, the tasks and hazards identified, the severity and probability ratings assigned, the risk levels reached, and the specific controls put in place.¹ Controls that were considered and rejected as infeasible should be recorded too, with the reasoning.

These records do real work. In a safety audit, they show that a structured process was followed rather than guesswork. After an injury, they show what hazards were known, what was done about them, and why the residual risk was believed to be acceptable. In litigation, the file can be the difference between a defensible position and a finding of negligence.

How OSHA and Courts Treat TR3

ANSI standards, TR3 included, are voluntary. The committees that write them have no enforcement authority, and skipping TR3 does not on its own trigger a fine. OSHA, however, references B11 standards when enforcing 29 CFR 1910.212, which requires that any machine creating a hazard be guarded to protect employees.² The regulation itself says guarding devices should conform to “any appropriate standards,” which pulls the B11 series in by reference.⁸

Even where no specific OSHA standard covers a machine, the General Duty Clause of the OSH Act requires every employer to provide a workplace “free from recognized hazards that are causing or are likely to cause death or serious physical harm.”⁹ ANSI standards are strong evidence that a hazard was recognized within the industry. An employer who ignored the B11 approach to risk assessment has a much harder time arguing the hazard wasn’t foreseeable. Courts also treat ANSI standards as evidence of the applicable standard of care in injury lawsuits, so noncompliance can produce civil liability on top of any agency penalty.

1
American National Standards Institute. B11.TR3-2000 (R2015) – ANSI Technical Report for Machines – Risk Assessment and Risk Reduction
2
Occupational Safety and Health Administration. Machine Guarding: Standards
3
ANSI. ANSI B11.0: Safety of Machinery
4
ANSI B11 Standards. B11.TR3 2000 (R2015)
5
CDC Stacks. Empowering Effective Teamwork for Machine Risk Reduction in the Workplace
6
CDC Stacks. Reducing Risk on Machinery: A Field Evaluation Pilot Study of Risk Assessment
7
American Society of Safety Professionals. Professional Safety – Risk Assessment and Reduction: A Look at the Impact of ANSI B11.TR3
8
eCFR. 29 CFR 1910.212 – General Requirements for All Machines
9
Occupational Safety and Health Administration. OSH Act of 1970 – Section 5 Duties