Assumptions: Show What Is Known and What Is Not

Human Performance weekly series: lesson 17 of 52.

A 5–10 minute crew discussion, plus time to verify the actual controls. The crew talk and Word version are public. Separate supervisor and attendance records are included with free Safety & Systems membership.

Why this matters

A statement can sound settled even when nobody has checked it: the replacement is equivalent, the route is available or the earlier result still applies. Make that uncertainty visible before another decision depends on it. Recording an assumption helps assign verification; it does not make an unknown condition safe.

Learning objective

Identify one assumption, record the consequence if it is wrong and establish who must validate it before the affected work relies on it.

Key hazards or failure points

Preliminary information treated as final; an old check applied to changed work; an expert’s confidence substituted for evidence; undocumented design judgment; an open assumption disappearing during a handoff.

Practical controls

• Write the assumption as a specific statement. Separate confirmed information from what remains unknown. Identify the work step or decision that depends on it and the possible consequence if it is wrong.
• Name the person authorized to validate it, the evidence needed and the point before which it must be resolved. Hold dependent work when a required condition remains unverified; do not create informal acceptance criteria.
• Track the outcome and its limits: supported, disproved or still unresolved. Carry restrictions into the work package and handoff. Changes to equipment, conditions or instructions may require the basis to be checked again.

Verify It in the Field

• Choose a nonhazardous planning example from today’s job. Ask what evidence supports the statement now. Locate its source and date, then check whether it covers the actual item and conditions. Record a missing basis honestly rather than filling it from memory.
• Ask the responsible technical role to identify the required validation method. Obtain the authorized safe check or review result without moving equipment or defeating protection for this exercise. Record the source, finding, checker, time and any stated limitations.
• Trace the outcome into the affected instruction or task record. Have the next person explain what may proceed and what remains held. Check that a pending review is not marked complete merely because someone has been assigned to it.

Stop and reassess

Hold the dependent decision or exposure when evidence is absent, contradictory, outdated or outside its stated scope. Seek the required authority. A crew vote, familiar practice or a successful previous job does not validate today’s required condition.

Crew discussion questions

• Which statement are we currently accepting without enough evidence?
• What changes if that statement is wrong?
• Who can validate it, and where will the result be recorded?

For each required control, record its acceptance source and criterion, safe verification method, responsible checker, actual result and time. Use VERIFIED, HOLD/NOT VERIFIED, or N/A with a reason. A tick alone is not evidence. Complete all applicable task inspections; do not enter danger or improvise a test to fill out a form.

Leader preparation and practical detail

Adapt the technical source without delegating engineering judgment

The DOE excerpt addresses scientific and engineering work, where documented assumptions may be used within a controlled technical analysis. This crew lesson helps workers recognize and route assumptions affecting their work. It does not authorize a supervisor or crew to invent a conservative design assumption, load rating or acceptance margin. If the work depends on an engineering determination, obtain that determination from the required technical authority and retain its conditions and limits.

A similar replacement needs an actual basis

Illustrative situation: a delivered component looks like the one used last time, so its suitability is described as obvious. Identify exactly what is being assumed and who can establish compatibility for the intended use. The validator examines the applicable approved documentation and product information; appearance alone does not close the question. Keep the dependent installation held when required evidence is missing. A purchase description or a colleague’s recollection may help locate information but is not automatically the required acceptance source.

Close the assumption without losing its limits

Illustrative situation: a planning assumption is validated for one route and one equipment configuration, then copied into another work package. The earlier result may no longer apply. Record the circumstances supported by the evidence and identify which changes require review. A useful closure tells the next person what was established, by whom, when and for which conditions. If validation disproves the assumption, revise the affected plan through the authorized process rather than editing the assumption to fit the desired answer.

Short supervisor field check

• Assumption stated separately from verified facts.
• Dependent step and consequence of a wrong assumption identified.
• Validation owner, evidence source and hold point assigned.
• Actual result and limitations recorded through the required review process.
• Decision, restrictions and need for revalidation reach the next user.

Confirm the relevant trained/authorized people, unresolved items, interim protection, correction owner and recheck. Record required release authority and rebrief anyone affected. The separate sheet supports these records; it does not replace a specialist inspection, permit or engineering determination.

Attendance and follow-through

Use the separate attendance sheet for participants, roles, discussion concerns, actions and late-arrival rebriefs. Attendance is not proof of competence, functioning controls or authorization to work. Keep completed records private under employer procedures.

Source acknowledgment

This resource draws on the U.S. Department of Energy’s DOE-HDBK-1028-2009, Human Performance Improvement Handbook, Volume 2 (June 2009). Todd Jerome Jenkins makes no claim of authorship or copyright ownership in the original U.S. Government work. New explanations, examples, exercises and layouts are Todd Jerome Jenkins adaptations. No endorsement by DOE or the U.S. Government is implied. Third-party material credited in the handbook remains attributed to its source; this notice does not claim rights in that material.

Source excerpt: Volume 2/VOLUME 2 VALIDATE ASSUMPTIONS.pdf; Printed pp. 22, 23. The June 2009 handbook supplies concepts; this lesson uses original explanations and exercises.

Technical scope and references

References reviewed October 9, 2026. DOE human-performance tools and OSHA recommended practices support preparation and discussion; they do not establish universal technical acceptance criteria. Apply the current task procedure, manufacturer instructions, permit and required competent or qualified decisions. A successful exercise does not replace required training, technical verification or work authorization.

1. DOE-HDBK-1028-2009, Volume 2 — Validate Assumptions, printed pp. 22–23 — June 2009 technical-work guidance adapted to crew recognition and referral. No authorization for workers to make engineering judgments; no generic hands-on check adopted.
2. OSHA Recommended Practices — Hazard Identification and Assessment — Guidance on relevant source information and assessment of changed work conditions.
3. HSE — Procedures — UK regulator guidance on controlled, usable procedures and their limitations; not a U.S. technical acceptance standard.

Connect this discussion to your JHA/JSA

Use the JHA/JSA planning and field-verification worksheet to record the actual task steps, hazards, responsible roles and controls. No task-specific worked example is linked for this topic yet. Return to What Changed Today? when the plan or conditions change.

Related Todd Jerome Jenkins articles: How to Conduct a Job Safety Analysis and What Is Human and Organizational Performance?.

Related crew discussions

• Job-Site Review: Does the Place Match the Plan?
• Questioning in the Field: Notice the Mismatch

Continue the weekly series

• Lesson 16: Questioning in the Field: Notice the Mismatch
• Lesson 18: Work Turnover: Transfer the State, Not Just the Story

Put one check into practice

Use the free JHA/JSA planning and field-verification worksheet to record today’s change, the required protection and the evidence needed before exposure.