Japan MHLW Adds 48 Workplace Chemical Exposure Limits From October 2027

The Ministry received 25 consultation submissions and made no changes to the proposal. The new limits build on 256 substances already covered, taking the notified total to 304. They also add zinc hexafluorosilicate to the existing entry for fluorine and water-soluble inorganic fluorine compounds.

Japan MHLW Concentration Standards Set Substance-Specific Thresholds

The 48 substances span refrigerants, corrosive alkalis, metals, pigments, pesticides and industrial intermediates. They include 1-chloro-1,1-difluoroethane, also known as HCFC-142b, sodium hydroxide, potassium hydroxide, tungsten, barium and zinc phosphate.

Representative values show why employers must work from the final substance table. HCFC-142b has an eight-hour limit of 1,000 parts per million. Sodium hydroxide and potassium hydroxide each have an eight-hour value of 1 milligram per cubic metre and a ceiling value of 2 milligrams per cubic metre.

The Ministry retained short-term protection for the alkalis because mist exposure can cause severe skin corrosion and eye damage even though the substances are solids under normal conditions.

The existing framework requires employers manufacturing or handling a listed risk-assessment substance indoors to keep worker exposure at or below the applicable value. Eight-hour and short-duration measurements, ceiling limits and the additive formula for mixtures continue to operate under the established rules.

What Changed And What Remains Unchanged

The legal change is the addition of 48 substance-specific limits and the related technical methods. The guidance integrates how to confirm exposure, select sampling and analytical techniques and choose effective respiratory protection. It does not replace the wider duty to minimise exposure to risk-assessment substances or the controls under Japan's special chemical regulations.

MHLW notes that about 80% of chemical accidents causing at least four days' absence arise from substances outside the special regulations. The self-directed risk-management system is intended to close that gap.

The caustic-alkali entries make mixture assessment especially important. This is an inference from the established additive approach. A workplace using sodium and potassium hydroxide together could meet each individual value yet still need to assess their combined effect because both can damage the same organs.

Practical Actions For Chemical Employers And Suppliers

Employers should screen inventories by substance identity and process, then identify tasks that can generate vapour, mist or inhalable particles. Occupational hygienists should validate detection limits, sampling media and mixture calculations before 2027 monitoring plans are fixed.

Suppliers should confirm identifiers and hazard information. Sites should test ventilation, containment and protective-equipment decisions against the new values. Contractors and laboratories need the same substance and task information because exposure evidence may cross organisational boundaries.

Foresight's occupational exposure limits topic tracks related workplace concentration standards and implementation changes.

Summary

Japan has finalised 48 new workplace concentration limits that apply from 1 October 2027. Employers should map affected substances now, validate sampling methods and reassess mixed exposures, including caustic mists, rather than treat the new values as simple safety-data-sheet updates.