Purpose and scope

EcoPro-Solutions and SEEF (UK) Ltd provide information, support and technical services for the safe management and control of hexavalent chromium (Cr(VI)). This briefing is written for chemists, HSE managers and maintenance and outage planners in the Energy-from-Waste (EfW) sector, one of the industries in which process-generated Cr(VI) is most consistently documented, yet to date least addressed by UK-specific regulatory guidance.

It sets out how and where Cr(VI) forms in EfW plants, the legal duties that apply, how it is reliably detected and treated, and how SEEF (UK)’s services, from toolbox talks through to laboratory analysis, support that work. It is intended as technical background, not as a substitute for a site-specific COSHH risk assessment.

All five conditions must coincide. EfW plants routinely bring them together in one place: chromium alloys, high temperatures, moisture, ambient air, and alkali and alkaline earth metals. That is why formation is so consistently documented in this type of plant. A 2024 study (Van Leeuwen) demonstrated the same mechanism: chromium vapours generated at high temperature reactively condense onto alkali- and alkaline-earth-bearing insulation to form stable Cr(VI) deposits.

Chromium-containing alloy: Stainless steel and other chromium-containing alloys are the chromium source; without chromium in the base metal, there is nothing to convert. Chromium can also be present in materials processed in the EfW plant.

Temperatures from ~250°C: At and above this threshold, chromium compounds begin to oxidise into the hexavalent form, consistent with SEEF’s own field observations on EfW plant.

Oxygen: Present in ambient air, oxygen drives the oxidation of Cr(III) to Cr(VI).

Moisture: Also present in ambient air, moisture converts the Cr(III) into a toxic and, in some cases, water-soluble form of Cr(VI).

Alkali and alkaline earth metals: Elements such as calcium, magnesium and sodium, common in mineral wool, insulation materials, refractory tiles and anti-seize pastes, are essential to the reaction. They act as a catalyst, which activates the transition process. They are also present in the waste that is burned.

In this briefing

• How Cr(VI) forms in EfW plants
• Your legal obligations
• Detecting Cr(VI) reliably
• Treating and controlling Cr(VI)
• How EcoPro-Solutions and SEEF support EfW operations

Think beyond the obvious: Cr(VI) can form in places where you would not expect it at first. For instance, where hot, alkali-containing ash reaches a stainless-steel conveyor belt, conditions in this location may be ideal.

Manufacturers in other high-heat sectors have acknowledged the same risk in their own safety bulletins, across power generation, gas and steam turbines, aerospace engines, marine propulsion and petrochemical plants. EfW is one instance of a wider, cross-industry issue.

How Cr(VI) forms in EfW plants

Chromium is a beautiful metal. When an alloy contains chromium, it forms a passive layer of Cr(III). This protects against corrosion, because the oxygen is bound to the Cr(III) layer and can no longer react with the iron. When the component is heated, that Cr(III) can oxidise to Cr(VI).

EfW plants contain large amounts of chromium-containing alloys. High-risk areas include steam boilers, superheaters, flue-gas ductwork, grate and furnace refractory-backed steelwork, turbines and standby generators: almost all of it thermally cycled, insulated, and opened during outages and fault clearance. Cr(VI) is also found in bottom ash conveyors and in fly and bottom ash.

Two formation routes matter on site, because they leave deposits in different places:

• Solid phase, at the surface. Cr(VI) forms directly on the hot steel surface and stays there as a solid deposit, in contact with the metal and the insulation touching it.
• Volatile, then condensing further away. Above roughly 300°C, volatile Cr(VI) gases can start to travel, for instance into and through the insulation. Where they reach cooler points and meet moisture, oxygen and alkali or alkaline earth metals (for example calcium from mineral wool), they condense as stable salts such as calcium or sodium chromate, often some distance from the hottest point. This also happens in other EfW processes, and the effect increases with temperature: at 600°C, over 100 times more volatile Cr(VI) escapes from the metal.

The common visible signal is a yellow chromate deposit on stainless steel and surrounding material, sometimes mistaken for sulphur compounds. However, Cr(VI) risk cannot be judged by eye: loose insulation dust with no visible colour change has been measured at over 50 µg of Cr(VI) per 100 cm². Assessment must rely on testing, not appearance. Where yellow or greenish colours are visible, a large amount of Cr(VI) compounds is present. For scale: 1 microgram is only 1/500th of a grain of sugar.

Airborne Cr(VI) dust: an inhalation pathway

Field observation during outages and insulation work confirms what the formation chemistry predicts: Cr(VI) does not stay where it forms. Solid-phase deposits on hot steel, and the chromate salts that condense within insulation, sit loosely in dust and fibre debris rather than being bonded to a surface. Any activity that disturbs that material can lift Cr(VI)-bearing particles into the air as a respirable dust: removing or cutting insulation, wire-brushing or grit-blasting scale, opening ductwork and casings, handling fly and bottom ash, or simply foot traffic and vibration during an outage.

This matters because inhalation, not skin contact, is the route of greatest concern for a genotoxic carcinogen with no safe threshold. Once airborne, the respirable fraction is not confined to the immediate work area. It can drift beyond the task zone, settle on adjacent surfaces, tools and PPE, and be resuspended by later disturbance, extending exposure to people who were never part of the original task. As with surface contamination, visible dust is not a reliable guide. A cloud of dust during insulation strip-out is obvious, but the finer, invisible fraction that reaches deep into the lungs is the greater hazard and gives no visual warning of its own.

Your legal obligations

In Great Britain, exposure to Cr(VI) is covered by the Control of Substances Hazardous to Health Regulations 2002 (COSHH), which require employers to assess and control exposure to carcinogens. Cr(VI) compounds are classified as carcinogenic (CLP category 1B, H350i) and skin sensitising (H317), with uptake by both inhalation and skin contact. Water-soluble Cr(VI) salts dissolve in sweat and can be absorbed through the skin, which is easy to underestimate.

The Workplace Exposure Limits in HSE guidance note EH40/2005 set two 8-hour time-weighted average values for chromium(VI) compounds, both in force since 17 January 2020. Cr(VI) arising as a by-product of work on hot, insulated components, as on EfW boilers and steam plant, is process-generated, so the higher of the two limits technically applies onshore.

This leaves the UK onshore limit as an international outlier. A WEL is a ceiling, not a safe target: COSHH still requires exposure to a carcinogen to be reduced to as low as is reasonably practicable (ALARP). With the UK’s own maritime regime and the EU both treating 5 µg/m³ as workable, staying just under set limits is difficult to defend as ALARP on its own.

Germany treats process-generated Cr(VI) on hot, insulated, chromium-alloyed components as a named, regulated risk, with a lead body (BG ETEM), a ready-made work instruction for insulation removal (BG BAU/GISBAU document 5459), and workplace measurement data going back over a decade. We are not aware of an equivalent UK regulator publication addressing this specific source in the same level of detail. Until one exists, we recommend that EfW operators set an internal control standard against the strictest relevant benchmark rather than the highest legal ceiling. This is both more defensible and more durable, since Cr(VI) limits only move downward.

Where exposure concentrates

Exposure concentrates at similar locations at every EfW site: around boilers, steam and gas turbines, industrial furnaces, standby generators, ductwork, bolts and within insulation. During outages and maintenance in particular, though not exclusively, Cr(VI) compounds can be disturbed and become airborne.

Detecting Cr(VI) reliably

Because Cr(VI) risk cannot be judged by eye, and because “no safe threshold” does not mean chasing zero, reliable detection is what turns a suspected risk into a manageable one. SEEF (UK) supports a three-step detection sequence, moving from a quick first screening test to a defensible quantitative result.

A positive swab result is informative. A negative result should not be taken as conclusive without confirmation by a definitive test method. Quick swab tests, irrespective of manufacturer, can deliver a false negative caused by chemical interference from metals such as zinc, aluminium and iron, all common in and around EfW plants.

The Dutch Labour Inspectorate (Nederlandse Arbeidsinspectie) reaches the same conclusion. It states that swab-type quick tests and handheld XRF measurements too often produce false positive and false negative results, and are not reliable enough to be used as the only test; they should be treated as a screening tool, not a stand-alone result. Under its guidance, a positive quick test can be enough on its own to justify taking all technically feasible control measures without delay, but a negative result is not sufficient grounds to conclude that no measures are needed. Quick tests remain a useful first screen.

The limitation in conventional laboratory testing

The interference problem that affects swab tests also applies to traditional laboratory methods, including NEN 5617, NIOSH 7600 and ISO 15192. During extraction of a Cr(VI) sample, the acids used can simultaneously release other metals from the matrix, such as zinc and aluminium. These metals readily donate electrons and reduce Cr(VI) to Cr(III) during the extraction, before the sample is measured. This interference results in systematic under-reporting of the true Cr(VI) level; in the presence of this kind of matrix interference, conventional methods often yield only semi-quantitative outcomes.

For an EfW operator, this matters directly. Paint systems, coatings, refractory materials, insulation debris, fly and bottom ash and general plant grime are exactly the kind of mixed-metal matrices in which this interference occurs. A report that says a surface is “below the limit” using a conventional method may simply mean the method could not see the Cr(VI) that is there.

Air monitoring: confirming airborne contamination

Surface swabs and bulk sample analysis establish whether Cr(VI) is present on a surface or in a waste stream. They do not establish whether it has become airborne, or at what concentration workers are inhaling it, which is the exposure that COSHH and the Workplace Exposure Limits in EH40/2005 are written to control. Confirming that requires air monitoring, not surface testing.

Personal (breathing-zone) sampling, using a calibrated pump and filter worn by the worker, gives the most direct evidence of individual exposure during a specific task. Static (area) sampling at fixed points around the work area shows how far contamination spreads, and whether it affects people who are not doing the work itself. Both rely on a validated method for hexavalent chromium in air, such as HSE MDHS 52/3 or NIOSH 7600, rather than the swab or bulk methods discussed above, which are not designed for airborne samples. Because of interference, every known method under-reports actual levels of contamination. SEEF is developing its own validated method for Cr(VI) in air, building on its patented analysis method, to deliver a reliable figure.

Timing matters as much as method. Airborne Cr(VI) concentration is driven by the disturbance activities identified above (insulation removal, grit-blasting, ash handling, outage maintenance), so monitoring should be planned around those tasks rather than run as a single, generic background measurement. A result taken outside the activity that generates the dust will understate the exposure it was meant to capture.

Air monitoring is also what turns a control judgement into evidence. Without a measured result against the relevant WEL, an employer can assert that a task is controlled to ALARP but cannot demonstrate it. For an EfW operator managing outages on a fixed schedule, air monitoring data is what justifies, or challenges, the containment, PPE and RPE specified for a given task.

Treating and controlling Cr(VI)

Managing Cr(VI) does not mean chasing zero, an unachievable and, for genotoxic carcinogens, scientifically meaningless goal. It means climbing the occupational hygiene control hierarchy as far as reasonably achievable and then confirming the result. The internationally recognised STOP framework structures that work:

Where surfaces or waste are contaminated, a chromate-reducing treatment converts Cr(VI) to the far less hazardous Cr(III). It should be applied using a recognised, tested neutraliser rather than an informal workaround such as acetic or ascorbic acid, as these acids do not transfer electrons effectively or efficiently.

A myth, tested and refuted: WD-40 does not neutralise Cr(VI)

SEEF regularly hears from customers in various sectors that WD-40 Multi-Use Product is used on site in the belief that it chemically reduces Cr(VI) to Cr(III). We tested this directly. WD-40 is a water-insoluble mixture of aliphatic hydrocarbons with no chemically reducing components, and no dose-dependent reduction in Cr(VI) was observed: recovery of an already-dissolved Cr(VI) solution remained at 96.8% after exposure to WD-40, and a reference paint sample showed no dose-response at all. A sharp drop in recovery, seen when solid Cr(VI) was brought into direct contact with WD-40, was traced to a solubility artefact: the Cr(VI) clumped in the oil phase rather than dissolving. It was not a chemical reaction.

For EfW maintenance teams, the practical takeaway is straightforward: treating a Cr(VI)-contaminated surface with WD-40, or a similar general-purpose oil, does not neutralise the hazard, however it may look on the surface. A recognised, tested Cr(VI) neutraliser is required, ideally confirmed with a follow-up test.

How SEEF (UK) supports EfW operators

SEEF (UK) Ltd provides information, support and technical services covering the full lifecycle of managing Cr(VI) risk on site: from raising awareness on the ground, through detection, to treatment and verification.

Why reliable data matters to an EfW operator

Cr(VI) control decisions (how a work area is contained, what PPE is specified, whether waste is classified as hazardous, whether a surface can be signed off as clean) are only as good as the data behind them. Where conventional testing under-reports Cr(VI) because of metal interference, those decisions are being made on an artificially reassuring number. SEEF (UK)’s role is to close that gap: reliable detection at every step, so that informed decisions can be made and defended.

Sources

German sources (BG ETEM, BG BAU/GISBAU, BG Verkehr, DGUV/IFA, BAuA/AGS) consulted and verified by SEEF, 3 June 2026. UK sources (HSE EH40/2005, COSHH, MCA MGN 624) verified 9 June 2026. Laboratory findings on matrix interference and on WD-40 are drawn from SEEF B.V.’s own validated method development and internal experimental studies (2026). Formation-mechanism detail, the Van Leeuwen (2024) study reference and SEEF laboratory volume statistics are drawn from SEEF B.V.’s fact sheet ‘Reliable detection of Hexavalent Chromium (Cr(VI)) in complex high-temperature insulation systems’. This briefing is provided as an independent technical knowledge source and does not replace a site-specific COSHH risk assessment