The Overlooked Ingredient, Overview

Markus Sommer

1. The facts

High temperature insulation contains basic oxides, above all calcium oxide and sodium oxide. Neither is classified as carcinogenic, and neither appears in any assessment of Chromium(VI). Above about 300 °C they react with the chromium oxide layer of chromium alloyed hot components to form calcium chromate and sodium chromate; sodium chromate already from about 200 °C. The reaction needs a chromium source, a basic oxide, oxygen and temperature. All four conditions are present in an insulated hot plant during normal operation. In the delivered state no chromate is present; it forms at the interface between insulation and component and forms again after every start up. It is released during maintenance, removal, cleaning, overhaul and dismantling, as dust that leaves the work area on tools, clothing, gloves and removed components.

2. What is documented

The formation pathway has been described in patent form since 1939. United States patent 2,176,687 expressly claims the production of calcium chromate and sodium chromate from a chromium source, lime or soda and oxygen. It is confirmed experimentally at the metal to insulation interface: in 2015 CaCrO₄ was identified on calcium silicate insulation and Na₂CrO₄ on sodium bearing insulation, with 160 mg Cr(VI) per square metre of contact area after 1,000 hours and 940 mg/m² after 5,000 hours. A barrier layer 3 to 4 µm thick prevented formation almost completely. The earliest manufacturer warning dates from April 1990 and was expressly extended to insulation and textiles in 1994. Operator and service documents from the years 2019 to 2025 describe the same process, with the temperature window and the calcium source. Added to this are our own site inspections and wipe and material samples taken since 2019 on engines, power plants, incineration plants, ships, vehicles and construction machinery.

3. Why it is overlooked

The collective term Chromium(VI) states the hazard correctly and conceals the cause. Behind every solid finding there is a salt, and the prefix of that salt names the reaction partner. Anyone who finds calcium chromate sees where the compound came from; where only Chromium(VI) is mentioned, that information stays unused.

The design of the documents adds to this. The safety data sheet describes the delivered state and carries no meaning for the assessment of a maintenance operation. In the data sheets of the fibre products calcium does not appear as a line of its own, although it is contained in the substance definition behind the CAS number. The third cause lies in the analysis. For thermal insulation there is no standardised method, the matrix is itself the reaction partner, and methods transferred from other matrices give results that are too low, down to almost zero. A negative result without a stated recovery rate for the same matrix says nothing about the content.

4. Incineration residues

With thermal insulation the formation can be prevented through the choice of material. With incineration residues that option does not exist, because the reaction partner is in the feed material and the feed material cannot be chosen. Calcium oxide is present in household waste at about 3 percent. Calcium chromate forms between 500 and 850 °C where the oxygen partial pressure is sufficient, and above 850 °C it is reduced again.

The critical phase is therefore not full load operation but shutting down for maintenance. Ash residues remain on the grate and on chromium alloyed hot components, the temperature passes through the formation window from above, and opening the plant admits additional oxygen. During the internal overhaul scaffolding is erected and grate components are walked on, surface treated, removed and replaced. Where the plant uses direct desulphurisation, calcium bearing sorbent is also injected into the furnace at about 900 °C or into the boiler passes at about 350 °C. For this field only the protective regime remains.

5. The duties in seven legal systems

German regulation is the reference in this analysis because it describes the case treated here expressly. The German TRGS 561 covers it under 5.9.3 and applies the protective regime as soon as a Chromium(VI) burden cannot be excluded. The German Hazardous Substances Ordinance requires in Section 6 paragraphs 2a to 2c the examination of whether hazardous substances can be released from the plant during the work, the use of external expertise where the employer lacks the knowledge and, where a technical investigation is needed, that investigation as a precondition for the work. Section 7 paragraph 1 prohibits starting the work before the risk assessment and the protective measures are in place.

European law sets the frame. Directive 2004/37/EC has required for more than twenty years that the nature, degree and duration of exposure be determined and that the further routes of exposure, including absorption through the skin, be taken into account. It applies in all Member States. Since 17 January 2025 a binding limit value of 0.005 mg/m³ has been in force for Chromium(VI) compounds.

France applies the same European framework with three particularities. Article R. 4412-61 of the Code du travail requires the employer to assess the nature, the degree and the duration of the exposure of the workers for any activity liable to present a risk of exposure to a carcinogen, and the assessment covers every route of exposure, including absorption through the skin. Article R. 4412-66 requires substitution as far as this is technically possible and requires the employer to record the result of the investigation in the document unique. The binding limit value is 0.001 mg/m³ over eight hours and 0.005 mg/m³ short term, five times stricter than the European value; compliance is verified at least once a year by an accredited body, and an exceedance stops the work at the workplaces concerned. The pre-work asbestos investigation under Articles L. 4412-2 and R. 4412-97 covers six domains, among them rolling stock, ships, aircraft and industrial installations, structures and equipment. For the named substance the duty to investigate before work begins therefore exists precisely in the classes of plant in which chromates form; for chromates it does not exist.

Switzerland is not a member of the European Union and has no chapter of its own for this case. The duties follow from Article 82 paragraph 1 of the Federal Act on Accident Insurance, which requires the employer to take all measures that experience shows to be necessary, that the state of the art makes applicable and that are appropriate to the given circumstances, and from the Ordinance on the Prevention of Accidents and Occupational Diseases: Article 3 for the measures and the review of their effectiveness, Article 6 paragraph 1 for information and instruction, Article 8 paragraph 1 for work involving particular hazards, Article 11a paragraph 1 for calling in occupational safety specialists where the company lacks the expertise, and Article 44 paragraph 1, which expressly covers substances hazardous to health that are handled or stored. Suva sets no MAK value for Chromium(VI) compounds because no carcinogenic threshold is known for them; the value of 0.001 mg/m³, calculated as chromium, exists only as a condition of an exemption permit under the Chemical Risk Reduction Ordinance. In its place stands the minimisation requirement under the STOP principle, with substitution in first place.

In the Netherlands Article 4.2 of the Arbeidsomstandighedenbesluit requires the assessment of the nature, the degree and the duration of the exposure as part of the risk inventory, even where such activities are not currently carried out; Article 4.17 requires the priority replacement of carcinogenic substances and processes as far as technically feasible, and the express prohibition on starting before the assessment is written, for asbestos, in Article 4.54a. The Dutch limit value is 0.001 mg/m³ expressed as chromium.

In the United Kingdom the prohibition on starting work is written without reference to a particular substance. Regulation 6(1) of the Control of Substances Hazardous to Health Regulations 2002 states that an employer shall not carry out work which is liable to expose any employees to any substance hazardous to health unless a suitable and sufficient assessment of the risk has been made and the resulting steps have been implemented. The workplace exposure limit under EH40 in its fourth edition 2020 is 0.01 mg/m³, and for carcinogens the COSHH Regulations require reduction to the lowest level reasonably practicable.

In the United States 29 CFR 1926.1126(d) requires every covered employer to determine the 8 hour time weighted average exposure for each employee exposed to Chromium(VI). The permissible exposure limit under 29 CFR 1910.1026 is 5 µg/m³ with an action level of 2.5 µg/m³, together with protective clothing, change and washing facilities and a ban on blowing down with compressed air. Procurement law adds to this: clause DFARS 252.223-7008 prohibits the delivery of items containing more than 0.1 percent Chromium(VI) by weight in any homogeneous material, and likewise the delivery of items where Chromium(VI) would have to be removed or reapplied in later sustainment phases.

None of these systems recognises a threshold below which the protective regime would cease to apply, and in all of them the sanction attaches to the duty that was not performed rather than to the harm that occurred. In France the fine under Article L. 4741-1 of the Code du travail is applied as many times as there are workers of the undertaking concerned, and the faute inexcusable of the employer requires, according to the Cour de cassation, that the employer had or should have had awareness of the danger and did not take the measures necessary to protect the worker from it. Australia shows the direction of travel: from 1 December 2026 Safe Work Australia no longer issues workplace exposure limits for non threshold genotoxic carcinogens, Chromium(VI) compounds included, and the duty to eliminate exposure or to minimise it so far as is reasonably practicable takes their place.

6. Limits of subsequent treatment

The reduction of Chromium(VI) to Chromium(III) is chemically possible and requires a suitable reducing agent, a suitable pH range, sufficient contact time and proof of effectiveness. The work instructions available do not state the conditions that the certificate of the testing laboratory expressly names, and proof of effectiveness for the insulation matrix does not exist. Verification of success rests on the colorimetric spot test, whose negative result the same testing body declares in writing to be unreliable; a field study found 869 ng Cr(VI) at the turbocharger while the spot test at the same point gave a negative result.

Penetrating oil does not reduce Chromium(VI); the chromate passes into the oil phase and is withdrawn from the measurement. Chromium(III) is moreover not an end state. The soluble Chromium(III) compounds carry the sensitisation marking Sh in the German MAK and BAT list 2026, which compounds are actually present after a treatment is determined nowhere, and with the reinstalled material the reaction partner returns to the hot component.

7. Order of magnitude

The expert analysis contains a projection of the occasions, not of the findings. Public manufacturer statements, fleet statistics and plant registers give, among others, 190,000 engines of a single series in the field, more than 100,000 engines sold from two further series, an active installed base of 44 GW at one gas engine manufacturer, more than 7,000 gas turbines from one manufacturer with a stated share of about half of the global base, around 7,300 coal fired units, around 109,000 ships, 6.16 million trucks above 3.5 tonnes in the European Union and 2,539 waste incineration plants in Europe, the United States, China and Japan.

With the maintenance and overhaul intervals applied here, this gives about 58,000 to 61,000 occasions per year in the industrial segments alone, plus millions of workshop visits whose relevant share is not quantified. What stands for assessment is therefore not an isolated event.

8. The duties in Germany

Section 31 names the reasons why this analysis cites predominantly German rules. This section brings together the German provisions in force in one place and gives the source for every statement. In doing so it repeats points that stand in their own context elsewhere, so that a company in Germany does not have to assemble the duties from the whole of the analysis.

The term hazardous substance also covers what only arises later

The German Hazardous Substances Ordinance does not attach to the purchase. Section 2 paragraph 1 number 3 counts among the hazardous substances “substances, mixtures and articles from which substances within the meaning of number 1 or number 2 arise or are released during manufacture or use”. Number 4 additionally covers substances and mixtures which, because of their properties and the manner in which they are present or used at the workplace, can endanger the health and the safety of the employees. A chromate that forms at the interface between insulation material and hot component is therefore covered, although nobody bought it and nobody wanted to manufacture it.

Substitution and the ranking of the measures

Section 7 paragraph 3 requires that, on the basis of the result of the substitution check, “substitution be carried out as a matter of priority”, namely by substances, mixtures, articles or processes which, under the respective conditions of use, are not hazardous or are less hazardous. Section 7 paragraph 4 orders the further steps: the design of the processes and low emission forms of use according to the state of the art, after that collective technical measures at the source of the hazard and organisational measures, and only then individual measures including personal protective equipment. Section 7 paragraph 5 sentence 2 provides that the use of burdensome personal protective equipment may not be a permanent measure.

What follows from this for a company in Germany

From the provisions named there follows a set of documents that can be examined. These include the documented risk assessment, drawn up by a competent person, for the material pairing of chromium-alloyed hot component and basic insulation material, and the substitution check carried out and reasoned under section 7 paragraph 3. They include the information from the party commissioning the work under section 5a and the technical investigation under section 6 paragraph 2c. They include the operating instruction and the annual instruction under section 14. They include the entry in the exposure register or its reasoning under section 10a in conjunction with the German TRGS 410, the arranging of the mandatory occupational health care and the classification of the waste according to its content.

9. The duties in the European Union

The national bodies of rules of the Member States transpose Union law. This section brings together what Union law itself requires, and in doing so separates occupational safety and health law from chemicals law and from waste law. Implementation is a matter for the Member States; for a company the duties arise from the respective national law.

Scope of Directive 2004/37/EC

Under Article 3 paragraph 1 the Directive applies “to activities in which workers are or may be exposed to carcinogens, mutagens or reprotoxic substances as a result of their work”. It thus attaches to the exposure during an activity. Article 2 letter a point i defines the carcinogen through the classification criteria of Annex I of Regulation (EC) No 1272/2008 and contains no restriction to substances that are bought, placed on the market or deliberately used. Calcium chromate and sodium chromate are classified in harmonised form as carcinogenic category 1B in Annex VI Part 3 of that Regulation.

The binding limit value

Annex III Part A of Directive 2004/37/EC carries the entry “chromium(VI) compounds which are carcinogens within the meaning of Article 2 letter a point i (as chromium)” with a limit value of 0.005 mg/m³ as a time weighted average over eight hours. A short term value is not laid down, and the notes column is empty. The transitional column names 0.010 mg/m³ until 17 January 2025 and 0.025 mg/m³ until the same date for welding and plasma cutting work and similar fume generating processes.

What follows from this

For a company in a Member State the duty arises from the national transposing law. The test applied by Union law is at three points stricter than the question of a measurement. The assessment under Article 3 paragraph 2 is activity-related and is to be repeated on any change in the conditions. Absorption through the skin is expressly to be included under Article 3 paragraph 3. The reduction under Article 5 paragraph 3 is tied to no threshold; it applies as soon as a closed system is not technically possible. A Member State may provide for stricter provisions; the Directive lays down minimum requirements.

10. The duties in the Netherlands

The Netherlands is a Member State of the European Union and has transposed Directive 2004/37/EC into the Arbeidsomstandighedenbesluit. The case of application dealt with here is not named as such there either. This section brings together the Dutch provisions in force and gives the source for every statement.

The term substance is neutral as to origin

Article 1.1 paragraph 5 letter b of the Dutch Arbeidsomstandighedenbesluit defines hazardous substances as “stoffen of mengsels waaraan werknemers bij de arbeid worden of kunnen worden blootgesteld die vanwege de eigenschappen van of de omstandigheden waaronder die stoffen of mengsels voorkomen gevaar voor de veiligheid of gezondheid kunnen opleveren”. The definition attaches to the exposure at work and to the circumstances in which they occur. Purchase, placing on the market and intended use do not appear in it.

The limit value of 0.001 mg/m³

The statutory limit value is set out in Bijlage XIII Part B2 of the Arbeidsomstandighedenregeling, the list of limit values laid down for carcinogenic substances according to the risk approach. The entry reads “Chroom (VI)-verbindingen (als Cr)” with 0.001 mg/m³ as a time weighted average over eight hours. A CAS number, a fifteen minute value and a skin notation are not entered. According to the explanatory note on Bijlage XIII, for substances which can occur as particles the value relates to the fraction sampled as inhalable dust.

What follows from this for a company in the Netherlands

From the provisions named there follows a set of documents that can be examined. These include the written assessment under Article 4.2 paragraph 1 for the material pairing of chromium-alloyed hot component and basic insulation material, and the seven items under Article 4.13 including the reasoning why a substitution is not technically feasible. They include the limit value laid down by the employer under Article 4.16 paragraph 2, in so far as no statutory value applies. They include the list under Article 4.15 with its forty year retention, the annual instruction under Article 4.19 letter a and the description of the waste under Article 10.39 of the Wet milieubeheer.

11. The duties in the United Kingdom

This section brings together the British body of rules in one place, as the three preceding sections do for Germany, the European Union and the Netherlands. Since 1 January 2021 the United Kingdom has no longer been bound by Directive 2004/37/EC. The governing provision, the Control of Substances Hazardous to Health Regulations 2002, is older than that Directive and continues to apply unchanged.

The territorial scope is divided. The COSHH Regulations 2002 and the Control of Asbestos Regulations 2012 carry the note “E+W+S” and therefore apply in England, Wales and Scotland; Northern Ireland has provisions of its own, built up with the same content, in the Control of Substances Hazardous to Health Regulations (Northern Ireland) 2003 and the Control of Asbestos Regulations (Northern Ireland) 2012. In waste law the four parts of the country go their own ways, each with its own regulations for England, Wales, Scotland and Northern Ireland. Unless stated otherwise, the information in this section relates to England and Wales.

The term substance does not attach to the classification

Regulation 2(1) determines what a “substance hazardous to health” is. Letter a covers every substance which meets the criteria for classification in a health hazard class under the CLP Regulation, and does so expressly “whether or not the substance is classified under that Regulation”. Letter b covers substances with a workplace limit value approved by the British authority HSE, letter d dust of any kind above the concentration named there. A chromate that forms at the interface between insulation material and hot component meets the criteria of letters a and b, without there having to be a supplier, a safety data sheet or a formal classification.

Prevention, replacement and what is reasonably practicable

Regulation 7(1) requires the exposure to be prevented or, so far as that is not reasonably practicable, to be adequately controlled. Regulation 7(2) makes the priority of replacement clear; Regulation 7(3) orders the further stages from the design of the processes through control at source to personal protective equipment. Regulation 7(4) letter b expressly requires “the adoption of suitable maintenance procedures”, letter c the reduction of the number of exposed employees, of the level and the duration of the exposure and of the quantity present at the workplace to the minimum required for the work. Section 30 reproduces the wording of paragraphs 1, 2 and 5.

What follows from this for a company in the United Kingdom

The duties begin before the work. Regulation 6(1) prohibits the start without a suitable and sufficient assessment, and Regulation 6(2) letter e names maintenance with the potential for a high level of exposure as a subject of assessment in its own right. An assessment that does not consider the formation pathway on insulated chromium-alloyed hot components, although the component materials and the operating temperatures are known, does not meet this requirement.

12. Appendix: insulation materials with basic oxides and where they are installed

The following commercially available insulation materials contain the basic oxides described, which can trigger thermochemical in-situ formation of the chromium(VI) compounds described. These are not assumptions, but conclusions drawn from manufacturer information, warning notices from users and my own field observations.

The complete tables, with the source given for each row, are in the appendix to the expert analysis.

13. What is to be done

Where the formation can be prevented, it is to be prevented. That follows from the order of precedence in Section 7 paragraphs 3 and 4 of the German Hazardous Substances Ordinance, from Article 4 of Directive 2004/37/EC, from Articles R. 4412-66 and R. 4412-67 of the French Code du travail and, in Switzerland, from the state of the art under Article 82 paragraph 1 of the Federal Act on Accident Insurance, and from Article 4.17 of the Dutch Arbeidsomstandighedenbesluit. In high temperature insulation substitute materials without alkali and alkaline earth metal oxides are available; the substitution check can therefore be carried out with a result.

Where the formation cannot be prevented, the work is to be organised as work with a carcinogenic substance, with investigation before work begins, a documented risk assessment, low dust working, extraction, zoning, separate changing and washing facilities, personal protective equipment and controlled disposal.

Cleaning and decontamination work for the single operation and do not remove the material cause. Where the calcium bearing insulation stays on the chromium alloyed hot component, the chromate forms again at the next thermal load.

Version 1.4, October 2026. The British limit is corrected to 0.01 mg/m³ under EH40 in its fourth edition 2020, and the section on the duties in the United Kingdom takes in the hazard statements. This overview reflects the state of the expert analysis and the summary in version 1.10, including the sections on France and Switzerland. The evidence, the references and the list of sources are given there.