Manganese, dust/fume/compounds (as Mn) appears as WES_reduced: previous WES TWA 1 (dust); 1/3 (fume) → WEL Inhalable 0.1; respirable 0.02 mg/m³ as Mn. Until 30 November 2026, WES remains the compliance reference. From 1 December 2026, WEL applies once implemented — verify with the WHS regulator for your jurisdiction.
What you are measuring
You are defending a dual-fraction WEL. Monitoring design should state:
- Target as Mn (elemental reporting basis agreed with the lab)
- Fraction: inhalable for comparison to 0.1 mg/m³ and/or respirable for comparison to 0.02 mg/m³
- That historical dust 1 / fume 1/3 results answer a different regulatory pair
- Whether task samples (grind bursts, confined weld) will be time-weighted into a shift TWA or reported as diagnostics
Do not invent a STEL for manganese if SWA has not published one for this listing. Do not file a single undifferentiated “Mn” mass against both WEL lines without stating fraction.
Site patterns that drive strategy
- Production welding — continuous fume; inhalable often primary, respirable may still matter for fine fume
- Confined / repair welding — short duration, high concentration; easy to miss on open-bay days
- Powered grinding / finishing — respirable-rich; fraction choice is critical near 0.02
- Mineral processing / milling — dust-dominant transfer and bagging
- Foundry melt / pour / shake-out — mixed aerosol
- Baghouse and duct maintenance — episodic but SEG-defining
Agree method colour (sampler conventions, digestion, ICP reporting as Mn) with the lab before mobilisation — cite method IDs in the report, not as marketing claims.
SEG walkthrough
Example survey plan for a fabrication shop with Mn wire and a grind booth:
- SEG A — production welders (full-shift personal; fraction per objective — often inhalable primary).
- SEG B — confined repair welders (task-based; may be separate SEG).
- SEG C — grinders (respirable priority where finishing dominates).
- SEG D — baghouse / maintenance.
- Covariates: consumable Mn content, current, booth LEV on/off, confined vs open, RPE worn (context only).
Pre-define “representative”: sampling only on mild-steel days when Mn wire is unused answers the wrong question.
Sampling strategy
- SEG definition from tasks and aerosol generation.
- Fraction-matched samplers — inhalable heads for 0.1; respirable cyclones for 0.02; dual-fraction on priority SEGs when both lines must be defended.
- Full-shift plus task-based grind / confined-weld samples.
- Flow, grit checks, blanks documented; note co-metals that affect interpretation.
- Process context — consumable ID, amperage band, LEV state, booth doors.
- Enough replicates across days and consumable lots.
Report as Mn explicitly. If clients also want oxide speciation or other metals, scope them separately.
Design detail worth writing into the plan
- Task samples during grind bursts and confined entry weld
- Clear RPE status during sampled tasks
- Diagnostic statics at booth face for capture — labelled diagnostic, not personal TWA
- Explicit statement when cobalt / other metals are co-sampled — separate listings, separate interpretation
Interpretation
- Planning phase (now): compare fraction-matched TWAs to 0.1 (inhalable) and/or 0.02 (respirable) mg/m³ as Mn.
- Compliance phase (from 1 Dec 2026, once implemented): the WEL pair are limits not to be exceeded for persons at the workplace.
- Non-detects: state LOD/LOQ relative to a meaningful fraction of the relevant WEL line.
- Variable shifts: document extrapolation assumptions.
- Peaks: report grind / confined-weld concentrations as diagnostics; do not invent a STEL.
- Old dust 1 / fume 1/3 data: useful context; not a substitute for the dual WEL comparison.
Dermal / ingestion pathways may matter for powders; air monitoring alone does not close every risk assessment.
Method hygiene (peer expectations)
- Cite laboratory method ID, fraction and “as Mn” basis
- Avoid unverified “AS X requires …” claims for this analyte
- Reconstructable SEG and fraction logic in field notes
- Separate compliance comparison from LEV diagnostics
- Do not present an inhalable result as meeting the respirable 0.02 line (or vice versa)
- Do not invent numbers beyond Inhalable 0.1; respirable 0.02 mg/m³ as Mn
Control hierarchy cues for recommendations
When results approach either WEL line:
- Eliminate / substitute — lower-Mn consumables; wet grind; closed powder transfer
- Engineering — on-torch extraction; booth LEV; enclosed milling transfer
- Administrative — consumable control; confined-weld permits; written open-time limits
- PPE — fitted RPE with change schedules — listed last
State what evidence would show the control worked (repeat fraction-matched personal TWAs on representative weld/grind days; capture checks).
Peak tasks vs TWA
Clients often ask whether a ten-minute grind burst “failed the WEL.” Answer in two layers:
- The WEL comparators are 8-hour TWAs: inhalable 0.1 and respirable 0.02 mg/m³ as Mn.
- Task peaks still drive control design; report them as diagnostics with explicit time-weighting assumptions; do not invent a STEL.
Common failure modes
- One Mn result filed against both fractions without sampler detail
- Full-shift sampling on a day without Mn consumables or grind
- Ignoring maintenance / baghouse SEGs
- Early-adoption claims without regulator confirmation
- Merging Mn interpretation into cobalt / cadmium / beryllium narratives without separate designs
- Quoting old WES 1 / 1/3 as if still the WEL pair
FAQ — technical
Must we always sample both fractions?
Sample the fraction that matches the WEL line you are defending for that SEG. Dual-fraction is often warranted on priority metal SEGs until controls are characterised.
Can historical fume 1/3 data stand in for respirable 0.02?
As narrative context, sometimes. As WEL compliance comparison, no — fractions and numbers differ.
Is biological monitoring in scope for this WEL article?
Not required for WEL air comparison. Treat biomonitoring as a separate scoped discussion if asked.
What is the minimum defensible n?
Enough to characterise consumable- and task-driven variability for the decision you are making. One light-fabrication day rarely ends a control argument near 0.02 mg/m³ respirable.
Dual-fraction decision tree (write into the plan)
Use this three-question gate before you mobilise:
- Which WEL line is the client defending for this SEG? Inhalable 0.1 as Mn, respirable 0.02 as Mn, or both?
- What aerosol does the task actually generate? Continuous weld fume, powered grind, ore transfer dust, or mixed foundry aerosol?
- What will the lab report say on the certificate? Fraction, “as Mn”, method ID, LOD/LOQ — agreed in writing before pumps leave the office.
If the answers disagree, stop and rewrite the plan. Filing an inhalable result against respirable 0.02 is a peer-review failure, not a formatting issue.
Sources
- Safe Work Australia, Changes to Workplace Exposure Limits – May 2025 (PDF): https://www.safeworkaustralia.gov.au/sites/default/files/2025-05/changes_to_workplace_exposure_limits_-_may_2025.pdf
- SWA WEL / WES changes page: https://www.safeworkaustralia.gov.au/safety-topic/managing-health-and-safety/workplace-exposure-limits-airborne-contaminants/changes-between-wes-and-wel
- `/workspace/wel/wes-to-wel-changes-2026.csv` — Manganese WEL Inhalable 0.1; respirable 0.02 as Mn
Technical support
Need a fraction-matched monitoring plan or report review against the incoming WEL pair? Start at [occhygiene.com.au](https://occhygiene.com.au).
