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Machine safety screening · AS/NZS 4024 series

Does this change affect the guarding?

Guarding failures often come from changes: a new cleaning task, a faster cycle, a bypassed interlock that became normal, or a control retrofit. This check screens whether the safeguarding basis needs to be revisited.

Start the screeningWhy guarding fails after changes
Pathway at a glance

Guarding change pathway

Machine guarding failures often come from changes: a new task, bypassed interlock, speed change or safety-function retrofit.

Machine change — does the guarding need revisiting? Three gates: a bypassed guard or interlock means restore first, then redesign the task; new access to a danger zone means rerun the risk assessment; a touched safety function means specify and validate PL or SIL performance. Otherwise verify stopping distances and document the decision. Machine change on the table Guard or interlock bypassed? yes Restore first then redesign the task no New access to a danger zone? yes Rerun risk assessment task-based, all modes no Safety function touched? yes Specify and validate PL / SIL performance no Verify and document stopping distances, records Red — act immediately · Amber — assessment needed · Green — record and proceed
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How to use this summary

  • A bypassed safeguard is an immediate control issue and a design finding.
  • Changed exposure means the risk assessment needs to be revisited.
  • Changed safety functions need specification and validation, not just wiring.
  • Even when no impact is indicated, record the decision basis.

This is a screening summary only — it is not a machine risk assessment or validation.

01

Screen the safeguarding impact

Route the trigger through exposure, safety functions and who owns the change before deciding whether to document, reassess or validate.

TriggerExposureSafety functionResult
Trigger

What is the trigger?

02

Why guarding fails after changes

The original guard may have been fine for the original task list. The problem is often that the task list moved.

01

The task list drifted

Machines accumulate tasks such as new products, cleaning regimes and maintenance routines that the original assessment never saw.

02

Speed changes break guard distances

Safety distances assume stopping performance; a VSD or drive change can quietly invalidate them.

03

Bypasses are requirements in disguise

Every defeated interlock marks a task the design did not accommodate well enough.

04

Safety functions need verification

Category, PL or SIL is a property demonstrated by design and validation, not a part number you buy.

03

Worked screening examples

01
Controls

Packaging line sped up 20%

Context: A drive swap increases cycle speed and changes run-down performance.

Screening view: The tool routes to functional-safety verification and guard-distance recheck.

02
Task change

New washdown task inside enclosure

Context: A fixed guard is removed weekly for cleaning because the task changed.

Screening view: The safeguarding basis has changed; reassess the task and design access with protection in place.

03
Bypass

Interlock taped over

Context: An interlock is defeated to clear jams on a bagging machine.

Screening view: Restore immediate control first, then treat the bypass as evidence of a design-task conflict.

04

Reference basis

This check paraphrases the machine-safety decision pathway; it is not a risk assessment or validation report.

AS/NZS 4024 seriesSafeguarding of machinery and risk-reduction pathwayWHS RegulationDuties of persons who modify plantAS Applied machine guarding checklistPractical checklist companion ↗
Important limitation

A screening framework for deciding whether safeguarding needs to be revisited — not a risk assessment, validation or confirmation that a machine is safe. Machine safety assessments for real plant need competent persons and, where engineering judgement is applied in Queensland, may involve the RPEQ pathway.

Get Engineering Help

Has a machine changed since the original guarding assessment?

XPO Engineers can help define the task list, review mechanical guarding impacts, and coordinate design evidence for plant modifications.

Ask an engineer