16. Manufacturer and operator warnings: documented state of industrial knowledge

The scientific works do not stand in isolation. Manufacturers of engines, generating sets, insulation materials and mineral wool have taken up the issue in technical information, service bulletins and safety instructions. These documents show that the formation pathway has been observed in practice in various industrial fields of application, confirmed analytically and in some cases linked to specific prevention requirements. These notices are not precautionary advice. They describe findings on plant in operation, in some cases with images from the field.

The earliest notice: Babcock & Wilcox 1990 and 1994

The first documented manufacturer warning concerning this formation pathway does not date from recent years. In April 1990 the Babcock & Wilcox Power Generation Group issued Plant Service Bulletin PSB-43 to owners and operators of boilers and steam generators. The first version concerned chromium-containing refractories. The revised version PSB-43A of March 1994 expressly extends the scope to “plastics, insulation, and textiles”. [75]

The bulletin describes the process unambiguously: materials used in boilers may contain chromium compounds “as part of the mixture or composition”, and “during operation, some of the chromium compounds may be converted to hexavalent chromium”. On removal, “the dust created may transport the hexavalent chromium. Inhaling hexavalent chromium increases the risk of lung cancer in humans”. [75]

The recommended measures correspond in substance to the protective regime that the German TRGS 561 sets out today under 4.1 and 4.2: training, equipment and monitoring of personnel, low dust working, no skin contact, disposal as hazardous waste, in the bulletin under 40 CFR 261 and 262. The difference lies in the trigger. The German TRGS 561 assumes in 3.3.4 and 5.9.3 that the formation of chromium(VI) compounds on chromium alloyed hot components cannot be excluded, and therefore requires the protective regime including the substitution check without prior measurement. The 1990 bulletin places an investigation at the beginning instead, recommending that before removal a qualified independent laboratory determine whether chromium compounds are present and whether they have been converted to chromium(VI). On replacement it states that substitutes for chromium-containing products are available, but that they sometimes have a shorter service life. [75]

The bulletin names the products concerned. Among the refractories and ramming mixes it lists Chrome Ore, Chrome Mortar, Kromight, Kromecast, Monochrome and Moldit Chrome Castable, among others. As chromium-containing insulation and textile products it lists Cerachrome, Z-Blok, Ceraform 130 and Cerachrome Felt. [75]

The conclusion that was drawn

The conclusion drawn was the obvious one: the product contained chromium, so chromium-containing products were deselected. The formulations themselves remained unchanged; the safety data sheet for Ceraform 130 still shows chromium(III) oxide at up to 3 per cent in its version of 23 December 2020 (Section 3). The yellow powder continued to appear. Since the chromium appeared to have been removed from the insulation, the chromium alloyed hot component remained as the explanation, and the finding was accepted as unavoidable. [77]

What was not recognised, a second time, was which compounds were involved. They were alkali and alkaline earth chromates, and their reaction partner had never been removed. It is still contained in the same products today, behind a CAS number that no user looks up. Present-day replacement solutions no longer have this problem: high temperature insulation materials free of alkali and alkaline earth metal oxides are available which avoid the formation pathway without loss of temperature resistance or service life.

What these warnings demonstrate

The warnings concern several industrial fields of application. MAN names calcium chromate and the material-related formation conditions; Frenzelit places its own calcium oxide contents in the same context. Caterpillar confirms actual Cr(VI) findings. Rockwool describes deposits and the basic oxide composition of its stone wool. [12-16]

Individual documents still declare the formation to be “not fully” understood or “generally not yet traceable” and refer to possible external sources such as spare parts, maintenance materials or operating environments. These statements may concern open questions regarding local source contributions, kinetics or specific operating conditions. They do not, however, call the documented formation pathway into question. Spare parts, assembly pastes and insulation materials in particular are possible carriers of the calcium and sodium compounds relevant to chromate formation.

Presenting the exposure as an isolated, inexplicable problem, or as one caused exclusively by external special circumstances, therefore disregards the published state of knowledge of science, manufacturers and the statutory accident insurance institutions. Whether such an omission is deliberate or unintentional cannot be derived from the documents themselves; technically, however, it has the effect of downplaying a known and avoidable reaction pathway.

Where the statement sits: the safety data sheets of the refractory products

HarbisonWalker International is the legal successor of Harbison-Walker, A.P. Green and NARCO, that is, of the manufacturers whose products the 1994 bulletin lists by name. The safety data sheets of its chromium-containing refractory products carry the sentence: “The chrome compounds (Cr III) in this product may be altered to a hexavalent compound (Cr VI) under certain use conditions, such as exposure to alkali salts and/or high temperatures.” It was checked on PLASTECH RUBY (version 02 of 1 April 2021), AUREX 30 SR (version 02 of 29 June 2018), SFG (version 02 of 22 March 2021) and RUBY (version 03 of 17 April 2020). [93]

The sentence sits in section 13, disposal. In the sheets examined, the word hexavalent appears nowhere else, neither in section 2 nor in section 10. Under Appendix D to OSHA 29 CFR 1910.1200, section 10 requires the “Possibility of hazardous reactions, including those associated with foreseeable emergencies” and the “Hazardous decomposition products”, and section 7 the “Precautions for safe handling”; table D.1 lists sections 12 to 15 as non-mandatory. The statement about the conversion therefore sits in the part of the sheet for which no content review is required. That part is read by the person who decides on waste classification, and that happens after removal. [94]

The compositions show that the alkaline partner is present in several of these products. SFG, a magnesia-chrome brick, lists magnesium oxide at 70 to 90 per cent alongside chromium(III) oxide at 20 to 40 per cent. RUBY lists sodium aluminate at 2.5 to 10 per cent alongside chromium(III) oxide at 2.5 to 10 per cent. THERMOLITH, a chrome mortar with 80 to 100 per cent chromium compounds and 2.5 to 10 per cent sodium silicate as binder, does not carry the statement. The manufacturer describes the alkali as something the product is exposed to from outside, while in several of its own products it is a constituent. [93]

On the fibre side both the statement and the partner are missing. Safety data sheet Morgan SDS 252 in the revision of 1 June 2015 covers Cerachrome and Z-Blok in the CR grade and lists the refractories, fibers, aluminosilicate under CAS 142844-00-6 at 95 to 100 per cent together with chromium(III) oxide at up to 3 per cent; section 10 gives “None” as decomposition products, and chromium(VI) does not appear anywhere in the sheet. In none of the fibre sheets examined does calcium appear as a line of its own, not even in the sheet for Ceraform 130. The reaction partner is hidden inside the substance definition behind the CAS number: the ECHA registration dossier describes the substance group as an amorphous glass fibre made of silicon dioxide and aluminium oxide with a number of further oxides, calcium oxide among them expressly, and the definition of the substance class allows an alkali and alkaline earth oxide content of up to 18 per cent by weight. [95, 96]

Two accounts of the same reaction therefore exist side by side. The refractory makers name the conversion path and its conditions and place the statement in the disposal section. On the fibre side the path is not named, and the reaction partner does not appear in the sheets as a constituent.

Safety information: as-delivered condition and condition in use

Rockwool's European ProRox WM-S/SW instruction already contains, as of 1 May 2023 and still in version 1.1 of 1 January 2025, express references to Cr(VI) deposits after high-temperature use, their cancer hazard and protective measures during removal. The European instruction refers specifically to versions with stainless steel mesh and/or stainless steel stitching wire. [16, 24]

For Morgan, the sections on reactivity mainly address the stability of the AES fibres, binder decomposition and high-temperature phase changes. Fibre and silica dust issues after use are also addressed; the reaction pathway with chromium-containing mating surfaces is not explained in the British SDS 418 examined. In the German article information on Pyrogel XTE, Aspen describes no known hazardous reactions under normal use, but does not mention a chromate pathway. This is a specific documentation gap for the further examination of suitable material combinations. It is not a finding about all documents of these manufacturers. [28, 29]

For the assessment, the as-delivered condition must be distinguished from the intended thermal application and from the condition on removal. A fibre not classified as hazardous, or a product treated as an article, may after use be contaminated with newly formed hazardous substances. The decisive question is whether the safety information covers this change of condition for the intended contact with chromium-containing components.

Manufacturer knowledge since 2019:

The author holds manufacturer correspondence from dating from August 2019. In it, the manufacturer informed its supplier of exhaust insulation that deposits between the exhaust insulation and exhaust pipes on engines had tested positive for chromium(VI). The matter was to be treated as a substance of very high concern (SVHC) with the highest urgency. Already at that time, the manufacturer identified as the cause the chromium-containing stainless steel, in particular the wire mesh of the insulation, reacting with calcium from the insulation material. It was additionally stated that the problem occurred on all engine types. [52]

The calcium-dependent formation pathway was thus known to the manufacturer almost four years before Technical Instruction (2023). It corresponds to the mechanism described by Udy 1939, Paoletti 2002 and Sayano 2015. [1, 11, 25, 50]