Process-Generated Cr(VI) in High-Temperature Environments: How It Forms and What Employers Need to Know #

When people think of chromium-6, they think of old paint layers on steel bridges, locks, window frames, and trains. That is an important part of the story, but not the whole story. In high-temperature environments such as engine rooms, gas turbines, biomass boilers, refractory furnaces, and steam crackers, Cr(VI) can form as a process by-product, without ever having been purchased as a raw material. The substance is generated through a reaction between the metal of the installation and the material surrounding it, driven by heat and moisture. For employers in industry, energy, and shipping, this is the least visible — and often the most underestimated — Cr(VI) risk.

What Is Process-Generated Cr(VI)? #

With paint, the material already contains Cr(VI) compounds before the paint is applied, and therefore also when it is later worked on, such as during sanding. With process-generated formation, Cr(VI) is not present initially; the substance forms during or after operation. The raw material is chromium from the metal of the installation itself: stainless steel, heat-resistant steel, chromium-containing alloys, or chromium-containing coatings. Under high temperature and in contact with certain reaction partners, this chromium converts to the +VI oxidation state, after which it deposits as a chromate salt in insulation, on surfaces, and in surrounding dust.

This makes this form of Cr(VI) difficult to predict and difficult to investigate in advance. When an installation is delivered, an employer sees no red or yellow coating (although it can of course occur in other colors); exposure only becomes apparent during maintenance, refit, or dismantling. Manufacturers of these installations are aware of this. Caterpillar, Siemens, GE Power, MAN Energy Solutions, MTU/Rolls-Royce, Innio, Frenzelit, and the European insulation industry organization EiiF have published technical bulletins and information sheets in recent years describing this phenomenon. For the party carrying out the work, however, this is often new information.

How Does Cr(VI) Form in High-Temperature Environments? #

Cr(VI) formation in high-temperature environments is not a random process. It requires a number of conditions to come together. Anyone who can recognize these conditions in their own installation immediately knows where the risks lie.

Five conditions for chromate formation:

1. A chromium-containing metal: stainless steel, chromium-containing heat-resistant steel, chromium-nickel alloys, or chromium-containing coatings.
2. High temperature: in practice, SEEF applies a threshold of approximately 250°C as the lower limit for relevant chromate formation. Reaction rate increases sharply at higher temperatures. Sayano-Kanno (2015) specifically describes calcium chromate formation around 500–600°C; this does not cover all mechanisms at work in high-temperature installations.
3. A reaction partner with alkali or alkaline-earth ions: sodium (Na), calcium (Ca), potassium (K). In practice, these originate from insulation materials, fuel, condensate, and ambient deposition.
4. Moisture or cyclical condensation: water vapor activates the reaction and transports the formed chromates away from the source.
5. Time and surface area: the longer an installation is in operation, the greater the chance of Cr(VI) accumulation in insulation and dust.

Reaction Partners in Practice #

The reaction partners come from a broader range than many employers expect. In SEEF’s case files, we have encountered, among others:

• Mineral wool and rock wool insulation (Na, Ca from the binder and base material).
• Calcium silicate insulation and refractory cements (Ca-rich).
• Fly ash and fuel residue in combustion installations (Na, K, Cl).
• Road salt, marine aerosol, and brackish water (NaCl).
• Dust from fertilizer or agrochemicals (Na, K, NH₄).
• Process residue and condensate with dissolved salts.
• Gaskets and sealing materials in high-temperature applications containing alkali binders.

Reaction Products and Mobility #

The chromate salts formed are not inert. They are water-soluble to varying degrees, which has direct consequences for the exposure route:

The combination of high water solubility and presence in dust has consequences for working on these installations. Wetting with water during dismantling — a common technique to limit dust — can, in the case of Cr(VI), actually open up a secondary exposure route via dripping and evaporating water. This risk is rarely addressed explicitly in standard dust-control protocols.

Where Do You Encounter Process-Generated Cr(VI)? #

The relevant target groups are found in industry, energy, shipping, and construction, in a range of usage situations. The overview below is not an exhaustive list, but presents the typical cases SEEF works with in practice, or for which the manufacturer itself has issued public warnings.

In the Netherlands, this topic is gaining attention among end users at a rapid pace, while regulation and sector frameworks are still largely geared toward paint work. A ship undergoing refit, a biomass boiler under maintenance, or a gas turbine being stripped down all fall under the same occupational health and safety duty of care as a paint remediation project today, but without a comparable protocol to rely on.

Why Beheersregime 2.0 Doesn’t Work Here #

Beheersregime 2.0 (Rijkswaterstaat, ProRail, and the Central Government Real Estate Agency, April 2022) is a valuable framework for planned maintenance of old steel protective coatings. For process-generated Cr(VI), it runs into difficulty on four points.

1. The thresholds are expressed in mg/kg in the dry paint layer. For insulation, refractory cement, or dust in an engine room, that unit and the associated sampling method do not apply one-to-one.
2. The types of work covered by Beheersregime 2.0 (manual sanding, mechanical sanding, burning, drilling) belong to paint remediation. Dismantling insulation, replacing a gasket, or cleaning dust in an engine room are not included.
3. Beheersregime 2.0 assumes that the Cr(VI) concentration can be determined representatively in advance. With process-generated formation, the distribution is by definition inhomogeneous and highly location-dependent.
4. The approach for the orange and red categories is built around static sources. With water-soluble chromate salts in a humid engine room, secondary exposure via condensate and skin contact comes into play — something not explicitly addressed in the regime.

What remains in force is the general framework: Article 3 of the Working Conditions Act (duty of care) and Chapter 4 of the Working Conditions Decree (carcinogenic substances). Substitution, the STOP strategy, 40-year registration, and periodic medical examination all apply in full. No sector matrix is available to determine the specific approach per situation; this requires a tailored solution for each case.

Investigation Strategy: Three Sample Types That Complement Each Other #

Because representative preliminary investigation does not work for process-generated Cr(VI) in the way it does for paint, SEEF uses three complementary sample types in these situations. Which combination is needed depends on the installation, the planned intervention, and the employer’s specific question.

Material Sample #

A collected piece of insulation material, refractory cement, dust, or gasket is quantitatively analyzed in the laboratory for Cr(VI) per kg of material. This measurement provides information about the substance itself: is Cr(VI) present, and at what concentration? For insulation and dust, SEEF uses matrix code HTI01. For the current state of validation, SEEF uses the detection limits from the related matrix AIR01 as a reference, supplemented where necessary.

Wipe Sample #

A standardized surface area (10 × 10 cm in accordance with ASTM D6966) is sampled and analyzed. The result is reported as µg Cr(VI) per surface area. Wipe samples are valuable for establishing whether a cleaned surface meets a target level, and for mapping spread within a space. In practice, SEEF applies a detection limit on the order of 0.1 µg Cr(VI) per 100 cm² for this purpose.

Air Sample #

During the work itself, exposure in the breathing zone is measured using personal sampling. For Cr(VI) in air, SEEF follows NIOSH 7600 as the basis (matrix AIR01). The choice of filter medium, flow rate, and sampling time is tailored to the specific task; SEEF advises on this per situation. A single measurement provides a snapshot; assessing compliance against the exposure limit in accordance with NEN-EN 689 requires multiple measurements per activity.

Site Visit and Collaboration with the Contractor #

The choice of sampling strategy cannot be determined remotely. For cases where the work is not planned in advance (such as a gasket replacement during a refit), SEEF joins the project on-site and coordinates sampling with the party carrying out the work. This prevents an investigation from being set up using a preliminary-investigation logic that does not hold up for process-generated Cr(VI).

What Must an Employer Arrange for Process-Generated Cr(VI)? #

The checklist from page A (“Chromium-6 Legislation in the Netherlands”) remains the starting point. A few points deserve extra attention with process-generated Cr(VI):

• Extend the risk assessment (RI&E) to the actual installation: look not only at what has been purchased, but at what can form under operating conditions. This applies specifically to installations with chromium-containing steel or stainless steel in combination with insulation, refractory cement, or combustion residue.
• Weigh substitution at the material-selection stage: do chromium-free or low-chromium alternatives exist for insulation, gaskets, and refractory cement? For some applications, yes; for others, not yet.
• Add a Cr(VI) section to maintenance, dismantling, refit, and dust-cleaning procedures, even if the installation shows no red or yellow coating.
• Account for dermal exposure. Water-soluble chromate salts can enter the body via skin contact, particularly during wet work, wetting procedures, or sweating.
• Treat dust in old plant rooms as a secondary source, even during non-active work such as equipment overhaul or inspection.
• Provide information to both own personnel and subcontractors: for many, process-generated Cr(VI) is an unfamiliar substance. Demonstrable instruction is especially important here.

How SEEF Works in These Situations #

SEEF’s patented method (WO2023219493) is designed to detect Cr(VI) selectively and quantitatively in complex matrices, even in the presence of interferents such as zinc, iron, copper, and aluminum. This tolerance to interference is particularly relevant for process-generated Cr(VI): fly ash, refractory cement, and engine-room dust contain a wide range of metals. A method that is not resistant to these interferences systematically underestimates the Cr(VI) concentration.

In addition to the analysis, SEEF provides on-site sampling, interpretation, and advice. For a typical shipping case, this means a walk-through with the contractor, identification of high-risk components, a combination of material and wipe samples prior to the intervention, and air measurements during execution. The report can be used for the employer’s own risk assessment (RI&E), for justification toward the client, and for coordination with the occupational health service and the Labour Inspectorate.

Where Does the Industry Stand Right Now? #

Process-generated Cr(VI) is well-documented scientifically. Karlsson (2012), Sayano-Kanno (2015), and Van Leeuwen (2024) describe the chemistry and the role of condensation. International manufacturers have been explicitly warning about it in technical bulletins for several years. In Dutch operational practice, this topic is gaining traction rapidly, but not yet with the level of awareness and the sector framework that exist for paint.

For employers, this means: don’t wait for a sector matrix to fulfill your own obligations. The occupational health and safety duty of care and Chapter 4 of the Working Conditions Decree apply regardless of whether a sector framework exists. For clients and maintenance companies, this is at the same time an opportunity to engage with the topic early; for employees, it explains why SEEF and partners are regularly present at installations that show no outward sign of the issue.

For the general legal context, see the page “Chromium-6 Legislation in the Netherlands.” For air exposure measurements, see “Cr(VI) Exposure Measurements.” For the selection of PPE and STOP measures, see “STOP Strategy, ALARA, and PPE for Cr(VI).” For specific questions about an installation or refit, SEEF can be contacted directly.

Sources and Background Literature #

Scientific literature and public information sheets

• Karlsson, S. (2012). Alkali-induced high-temperature corrosion of stainless steel: studies in the laboratory and in the field. Describes the reaction mechanism between alkali (Na, K) and chromium-containing steel under high temperature.
• Sayano-Kanno et al. (2015). Describes the formation of calcium chromate in high-temperature contexts (on the order of 500–600°C).
• Van Leeuwen (2024). Describes the influence of condensation and water vapor on chromate formation and mobility.
• EiiF (European Industrial Insulation Foundation), Information Paper: Chromium(VI) compounds in technical installations. Publicly available via eiif.org.
• Rockwool, Cr(VI) Safe Use Instruction Sheet. Publicly available via rockwool.com.
• ASTM D6966, Standard practice for collection of settled dust samples using wipe sampling methods.
• NIOSH 7600, Method for hexavalent chromium in air (basis for SEEF’s AIR01 matrix).

Manufacturer bulletins (available on request from SEEF)

Various international manufacturers of gas turbines, diesel engines, gas engines, gaskets, and industrial installations have published technical bulletins and information sheets in recent years on Cr(VI) residue in and around their installations. These include Caterpillar, Siemens, GE Power, MAN Energy Solutions, MTU/Rolls-Royce, Innio, and Frenzelit. SEEF holds copies of these bulletins and can share quotations and specific references on request, to the extent the manufacturer itself permits publication.

For current legislation and regulation regarding Cr(VI) and lead, see the page “Chromium-6 Legislation in the Netherlands.”