How the intentional engineering of a lower-toxicity, fully specification-compliant aviation fuel changes the legal obligations of helicopter manufacturers and military operators under UK health and safety law, and why the cost of inaction now outweighs the cost of adoption.
This white paper examines the legal and engineering implications, under UK law, of the availability of DoC Jet A-1, a fully specification-compliant aviation turbine fuel that is intentionally engineered through post-processing to remove polycyclic aromatic hydrocarbons (PAHs), including naphthalene, to levels far below those found in standard Jet A-1. DoC Jet A-1 meets ASTM D1655 and DEF STAN 91-091 in every respect. It is not a novel or experimental fuel: it is the same Jet A-1 specification delivered at higher quality, with an enhanced Certificate of Analysis that includes naphthalene content below 85 ppm as a documented, supplied property, not a future target.
The paper argues that the existence of this fuel, available now, under the existing regulatory framework, materially changes the legal calculus for helicopter OEMs and military operators under the ALARP principle and the common law duty of care. Drawing on the ongoing UK Ministry of Defence lawsuits brought by retired aircrew over chronic carcinogenic exposure on platforms including the Sea King, Puma, and Chinook, the paper makes the case that a drop-in, fully certified lower-toxicity fuel that requires no hardware change and no additional approval is, under UK health and safety law, an ALARP-relevant mitigation that manufacturers and operators are now legally obligated to formally evaluate and document.
The paper also examines a significant and as-yet unrecognised regulatory anomaly: the naphthalene content of standard Jet A-1, an IARC Group 2B possible human carcinogen permitted at up to 30,000 ppm in aviation fuel, while regulated to a maximum of 0.1% (1,000 ppm) in industrial hydrocarbon solvents such as Stoddard solvent. DoC Jet A-1's delivered naphthalene specification of less than 85 ppm places it below the industrial solvent regulatory limit, a meaningful marker in the occupational health record of any operator who adopts it.
UK military helicopter litigation and its implications for fuel selection obligations
In May 2024 the Guardian reported that the UK Ministry of Defence faces legal action from retired military aircrew alleging long-term exposure to carcinogenic exhaust fumes from military helicopters including the Sea King, Puma, and Chinook.[1] The claims centre on benzene (IARC Group 1 carcinogen), formaldehyde (IARC Group 1), polycyclic aromatic hydrocarbons (PAHs, including IARC Group 2A/2B classified compounds), and combustion-generated fine particulates, all products of burning standard Jet A-1 in conditions where rotor downwash recirculates exhaust into crew occupied zones.[2]
The litigation is not unprecedented. The aerotoxic syndrome litigation in the commercial fixed-wing sector, primarily concerning organophosphate contamination from engine oil seal failures, has over two decades shifted the burden of proof from claimants to manufacturers and operators. The rotary-wing litigation now emerging follows a similar trajectory, but with a crucial difference: unlike the bleed air contamination pathway (which requires structural hardware redesign), the PAH and aromatic exposure pathway is directly addressable at the fuel level. The PAHs, naphthalene, and aromatic compounds that drive the toxic exposure profile are properties of the fuel, not the aircraft, and they can be reduced through intentional post-processing of the fuel before delivery, without any change to the aircraft whatsoever.
What makes the current litigation particularly significant is the disclosure dimension. Legal filings and Freedom of Information disclosures have established that officials within the MoD and at OEM contractors were aware of the risks of toxic exhaust inhalation from military helicopters as early as 1999.[3] For manufacturers and operators who have not yet conducted formal evaluations of fuel-based exposure mitigations, the clock on foreseeability has been running since at least that date.
The military helicopter litigation changes the foreseeability threshold for all helicopter OEMs. Where previously it might have been arguable that chronic aromatic and PAH exposure from fuel combustion was an unforeseeable occupational hazard, the published litigation, the 1999 internal awareness documents, and the subsequent body of occupational health research make that argument untenable. For any helicopter manufacturer or operator who has not conducted a formal evaluation of fuel-based exposure mitigation from this point forward, foreseeability of harm is, in substance, established by the public record.
Standard Jet A-1 contains total aromatic hydrocarbons in the range of 15–20% by volume, with the specification permitting up to 25%. These aromatic species, which include benzene, toluene, ethylbenzene, xylene (the BTEX compounds), naphthalene, and heavier polycyclic aromatics, serve thermodynamic and materials compatibility functions in the fuel but contribute the majority of the toxic vapour and combustion-product load encountered by personnel.
The exposure pathway in rotary-wing operations is qualitatively different from fixed-wing for three reasons. First, helicopters operate extensively in hover and low-speed flight, conditions at which engines produce the highest specific particulate emissions per unit of fuel burned, as incomplete combustion at partial power generates disproportionate soot and PAH yields. PAHs are, by their chemical nature, more resistant to complete oxidation than the paraffinic and cycloparaffinic fractions of jet fuel: their aromatic ring structures require higher combustion temperatures for complete breakdown, and at the partial-power conditions of helicopter hover, a substantial fraction survives as unburned and partially-combusted PAH species in the exhaust stream. Second, the rotor downwash characteristic of helicopter operations creates a well-documented aerodynamic recirculation zone that draws exhaust gases from the engine efflux back into the cabin and cockpit through open door apertures, fresh air inlets, and pressurisation intakes.[5] Third, military helicopter crew accumulate thousands of flying hours over careers of 15–25 years, creating a chronic cumulative bioaccumulation pathway for lipophilic compounds such as the heavier PAHs, which are stored in fatty tissue and the liver.
As Low As Reasonably Practicable: how the arrival of a certified drop-in lower-toxicity fuel resets the legal baseline for helicopter manufacturers and operators
The ALARP principle is embedded throughout UK health and safety law. It derives from section 2 of the Health and Safety at Work etc. Act 1974 (HSWA), which imposes on employers a duty to ensure the health, safety, and welfare at work of their employees "so far as is reasonably practicable." The same formulation appears in the Control of Substances Hazardous to Health Regulations 2002 (COSHH), which specifically require employers to prevent or, where prevention is not reasonably practicable, to adequately control exposure to hazardous substances, including carcinogenic chemicals encountered in the course of work.
The HSE's definition of ALARP requires that a risk be reduced until the incremental cost, time, and difficulty of further reduction become grossly disproportionate to the safety benefit achieved. Where a carcinogen is involved, the HSE operates an effectively zero-tolerance approach: employers are expected to reduce exposure to as close to zero as is technically and operationally feasible. Under COSHH Regulation 7, specific additional obligations apply to carcinogens and mutagens: employers must replace the substance with a less hazardous one if it is reasonably practicable to do so.
For aviation fuel, the COSHH carcinogen substitution duty has historically been dormant: no drop-in alternative fuel with substantially reduced carcinogenic content existed. The existence of DoC Jet A-1, a fuel already certified to ASTM D1655 and DEF STAN 91-091, requiring no hardware modification, and delivered with a chain-of-custody Certificate of Analysis that confirms naphthalene below 85 ppm, activates the COSHH substitution obligation. The question is no longer whether a suitable substitute exists. It exists. It is available. It is certified. The question is now why it has not been evaluated.
The ALARP assessment is not static. What constitutes a reasonably practicable mitigation changes as the state of the art advances. Prior to the availability of a certified drop-in low-aromatic fuel, the principal engineering mitigations for crew exhaust exposure in rotary-wing operations were mechanical: repositioning exhaust nozzles, installing exhaust diverters, modifying fresh air inlets, redesigning rotor-hub geometries. These modifications are costly, require type certificate amendments, extend over multi-year development programmes, and impose weight and performance penalties.[3] In this environment, a manufacturer or operator could credibly argue that the cost of further mitigation was grossly disproportionate to the risk reduction achievable.
That argument is no longer available in the same form. The state of the art has advanced. A specification-compliant drop-in fuel that reduces total aromatic content by 43–57%, reduces naphthalene from approximately 10,000 ppm to below 85 ppm, and demonstrably reduces non-volatile particulate matter (nvPM) soot emissions by 20–45% is now available under ASTM D1655 and DEF STAN 91-091. It requires no hardware modification, no type certificate amendment, no maintenance schedule disruption, and no change to supply or dispensing infrastructure. In ALARP terms, a mitigation measure this operationally frictionless sets a new baseline. It defines what is reasonably practicable. An organisation that declines to evaluate it, or that evaluates it and cannot document a reasoned justification for non-adoption, is accepting a foreseeable legal exposure that formal evaluation would eliminate.
Before DoC Jet A-1: Achievable exposure mitigation required structural airframe modification, type certificate revision, and a multi-year engineering programme. The argument that cost was grossly disproportionate to benefit was tenable.
After DoC Jet A-1: A drop-in, ASTM D1655 / DEF STAN 91-091 certified fuel with 43–57% lower aromatic content, naphthalene delivered at <85 ppm on the chain-of-custody CoA, and 20–45% lower nvPM soot production is commercially available now, with no modification to aircraft, infrastructure, or maintenance procedures. The cost of non-adoption is the burden that must now be justified. The cost of adoption no longer provides a disproportionality defence.
COSHH Regulation 7 establishes a hierarchy of controls for hazardous substances, in order of preference: elimination, substitution, engineering controls, administrative controls, personal protective equipment. For carcinogens and mutagens, Regulation 7(3) specifically requires that the employer replace the substance with a less hazardous one where it is reasonably practicable to do so.
Naphthalene, benzene, and formaldehyde, all present in or produced by combustion of standard Jet A-1, are classified carcinogens. Benzene carries an IARC Group 1 classification; formaldehyde was upgraded to IARC Group 1 in 2009; naphthalene carries IARC Group 2B. Under COSHH's substitution principle, an employer who knows that a lower-carcinogenic alternative fuel meeting all operational specifications is available and delivered under the same regulatory framework, and who does not formally evaluate its adoption, is in prima facie non-compliance with COSHH Regulation 7(3). DoC Jet A-1, certified to ASTM D1655 and DEF STAN 91-091 and delivered with a CoA confirming naphthalene <85 ppm, is precisely that alternative.
In UK product liability law, a manufacturer's liability is assessed against the standard of a product that is reasonably safe for its foreseeable use by its foreseeable users. For military helicopter OEMs, the foreseeable users are aircrew and maintainers who will accumulate thousands of hours of exposure to fuel vapour and combustion products over careers spanning decades. The foreseeable use includes hover, low-speed flight, hot-loading with rotors running, and ground-run engine testing, all of which generate elevated aromatic and PAH exposure through the rotor downwash recirculation mechanism.
A manufacturer who designs an airframe intended for prolonged military hover operations, whose fuel burns standard Jet A-1 generating approximately 10,000 ppm naphthalene and 15–20% total aromatics in the exhaust environment, and who has not formally evaluated a certified alternative delivering less than 85 ppm naphthalene on its chain-of-custody documentation, cannot credibly argue that the carcinogenic risk to the foreseeable user was either unforeseeable or unmitigable. Notice of a risk, combined with the availability of a certified mitigation, without subsequent documented evaluation, is the architecture of a negligence claim.
OEM and operator obligations to aircrew and maintainers under UK common law and the developing military helicopter litigation
The common law duty of care, originating in Donoghue v Stevenson [1932] AC 562 and developed extensively through product liability jurisprudence, requires manufacturers to take reasonable care not to cause foreseeable harm to foreseeable users of their products. OEMs owe a duty to design, test, and certify aircraft that are reasonably safe under foreseeable operating conditions, and to warn operators of residual risks that cannot reasonably be designed out.
The duty of care in the context of fuel composition has historically been treated as narrow: the OEM specifies the fuel standard (ASTM D1655, DEF STAN 91-091), the operator procures a compliant fuel, and which specific fuel within that standard is used has been treated as an operator procurement decision. This framing is now legally vulnerable. Where an OEM knows that the foreseeable use of its aircraft involves chronic exposure to carcinogenic PAH combustion products, and where a fully specification-compliant fuel with substantially lower carcinogenic content is available and delivered under the same ASTM D1655 and DEF STAN 91-091 framework, the question of which fuel is used becomes a duty-of-care question, not merely a procurement decision.
Critically, the duty here does not require OEMs to pursue experimental or novel fuel types. DoC Jet A-1 is not a new category of fuel. It is standard Jet A-1, delivered to a higher purity standard. The OEM's duty is simply to formally acknowledge its availability and compatibility, and to communicate that to operators. The cost of that action is negligible; the legal protection it affords is substantial.
The aerodynamic mechanism by which helicopter exhaust gases re-enter the cabin and cockpit through rotor downwash is well documented in OEM flight test reports and aerodynamic simulation outputs.[5] The phenomenon is not a manufacturing defect; it is an inherent consequence of the physics of rotary-wing hover flight. Rotor downwash generates a toroidal recirculation pattern that, depending on wind conditions, rotor speed, and aircraft geometry, draws engine exhaust gases forward into the fuselage zone and thence into open door apertures and fresh air inlets.
OEM aerodynamicists are fully aware of this phenomenon; it appears in flight test reports, CFD models, and exhaust plume characterisation documents produced during the type certification process. The recirculation hazard therefore meets the foreseeability standard for duty of care purposes. An OEM who certifies an aircraft for military operations, knows the aircraft will be operated in sustained hover with cabin doors open (standard tactical configuration), knows rotor downwash draws exhaust gases into the occupied zone, and has not formally evaluated a lower-toxicity certified alternative fuel as a mitigation measure is accepting a foreseeable liability risk that a fuel evaluation would substantially reduce at near-zero cost.
The PAH component of this exposure is particularly relevant. As described in Section 6 of this paper, PAHs in the combustion exhaust are not merely a residue from the liquid fuel but a product of the fuel's incomplete oxidation, and the yield of unburned PAHs is directly related to the PAH precursor load in the fuel. A fuel from which the PAH fraction has been intentionally removed, as is the case with DoC Jet A-1, produces correspondingly lower PAH combustion products under partial-power hover conditions. The engineering relationship between fuel PAH content and exhaust PAH yield is not speculative; it is a consequence of combustion chemistry and is measured and documented in the TERC test programme.
Legal filings in the UK military helicopter litigation have established, through disclosure documents, that the risks of toxic exhaust inhalation from military helicopter operations were raised internally within the MoD and by OEM contractors as early as 1999. This internal awareness is legally significant for two reasons.
First, it establishes that the hazard was subjectively known to the responsible parties, not merely objectively foreseeable. In negligence law, actual knowledge of a foreseeable risk that is not acted upon is treated more seriously than constructive knowledge. Where documents show internal discussion of the risk followed by inadequate action, the inference of breach of duty of care is substantially easier to draw.
Second, the 1999 awareness threshold creates a potentially long period during which, it can be argued, every retiring aircrew member with a health condition attributable to chronic aromatic and PAH exposure may have a limitation-period claim running from the date of diagnosis (under the Limitation Act 1980, section 14A). This substantially increases the systemic financial exposure of both the MoD and OEM contractors, and underlines the importance, for any organisation still using standard Jet A-1, of opening a formal documented ALARP evaluation of the available certified alternative without further delay.
For helicopter OEMs operating in the UK market after the publication of the military helicopter litigation and the 1999 internal awareness documents: the foreseeability of harm from chronic PAH and aromatic exposure in rotary-wing operations is, in substance, established. The legal standard now required is not merely that the OEM has not caused the harm; it is that the OEM has taken positive, documented steps to evaluate and reduce that harm to ALARP levels. DoC Jet A-1, certified to ASTM D1655 and DEF STAN 91-091, requiring no modifications, delivered with a chain-of-custody CoA confirming naphthalene <85 ppm, provides the specific, readily available mitigation that a formal ALARP evaluation would identify. Absence of that evaluation leaves the OEM exposed to the argument that it was aware of the risk and chose not to act.
For operators of military and commercial helicopters, primarily the armed forces, emergency services, and air ambulance operators; the duty of care analysis is overlaid by employer liability obligations under the HSWA and COSHH. These statutory duties are non-delegable: an employer cannot discharge the duty by pointing to the manufacturer's specification or the fuel supplier's standard. The employer's obligation under COSHH is to assess the risk (Regulation 6), to prevent or control exposure (Regulation 7), and to maintain and monitor control measures (Regulations 9–11).
An operator who has not formally risk-assessed the naphthalene, benzene, and PAH content of the fuel burned in its helicopter operations, and who has not formally evaluated whether a lower-toxicity certified alternative was available and reasonably practicable, is prima facie in breach of COSHH Regulation 6 (risk assessment) and Regulation 7 (substitution for carcinogens). The fact that fuel procurement has historically been handled at a logistics rather than an occupational health level does not discharge this obligation. DoC Jet A-1 is now a matter of public knowledge within the aviation fuel supply chain, delivered under the same ASTM D1655 and DEF STAN 91-091 framework as every other Jet A-1 supply. Ignorance of its existence, from this point forward, is not a defence.
An unrecognised regulatory anomaly: a compound regulated to 0.1% in industrial solvents is permitted at 3.0% in aviation fuel burned by personnel working in confined spaces
Naphthalene (C₁₀H₈) is a bicyclic aromatic hydrocarbon (and the simplest member of the PAH family) that occurs naturally in crude oil and concentrates in the middle distillate fraction from which jet fuel is refined. In standard Jet A-1, naphthalene is present at concentrations of approximately 7,800–11,800 ppm by volume, though the DEF STAN 91-091 and ASTM D1655 specifications permit up to 30,000 ppm (3.0% v/v). These specification limits were established to protect the fuel's smoke point and thermal stability during combustion; they reflect a combustion performance rationale, not a toxicological one. The possibility that the personnel handling and breathing products of this fuel over long careers might be chronically exposed to a Group 2B carcinogen at concentrations roughly 8 to 30 times the industrial solvent limit was simply not the parameter being managed.
Standard refinery processing does not target naphthalene for removal, because there is no specification incentive to do so. Naphthalene therefore remains in the fuel at whatever concentration the refinery feedstock produces, subject only to the upper limit and the smoke point test. The result is that every litre of standard Jet A-1 delivered to a military or civil helicopter operator contains naphthalene at a concentration that, in any other industrial product used by workers in proximity, would require either substitution or formal COSHH risk assessment and control.
The International Agency for Research on Cancer (IARC) classifies naphthalene as a Group 2B agent (possibly carcinogenic to humans), based on sufficient evidence of carcinogenicity in experimental animals and limited evidence in humans (associations with haemolytic anaemia, multiple myeloma, and urinary bladder cancer in occupationally exposed workers). The European Chemicals Agency (ECHA) classifies naphthalene as Carc. 2 (may cause cancer) under CLP Regulation (EC) No 1272/2008.
The UK Workplace Exposure Limit (WEL) for naphthalene vapour is 10 ppm (8-hour TWA), with a short-term exposure limit of 15 ppm (EH40/2005 and subsequent amendments). These limits were established on the basis of acute toxicity endpoints. No WEL has been defined below which the carcinogenic risk from naphthalene is considered zero; for IARC Group 2B substances, the precautionary position is that no entirely safe level can be assumed, and ALARP reduction is therefore applicable across the full exposure range, not merely above the WEL ceiling.
Additional classified carcinogens present in or produced by combustion of standard Jet A-1 include benzene (IARC Group 1; UK WEL 1 ppm TWA), present as a trace component of the aromatic fraction and formed during combustion, and formaldehyde (IARC Group 1; UK WEL 2 ppm ceiling), a primary combustion product of aromatic hydrocarbons at partial oxidation conditions. Both are produced in greater quantities from high-aromatic fuel combusted at the partial-power, partial-combustion conditions characteristic of helicopter hover operations, precisely because high-PAH fuels produce more intermediate species during incomplete combustion.
The most striking illustration of the regulatory gap is the contrast between aviation fuel naphthalene limits and those in comparable hydrocarbon solvent products. Stoddard solvent (white spirit, Type 1, CAS 64742-88-7), a petroleum-derived hydrocarbon solvent used in industrial degreasing, dry cleaning, and parts washing, is regulated under UK and EU chemical safety frameworks to a maximum naphthalene content of 0.1% by weight (approximately 1,000 ppm). This limit was established specifically to control carcinogenic hazard to industrial workers using the solvent in proximity.
The Jet A-1 specification permits naphthalene at up to 30,000 ppm, 30 times higher than the industrial solvent limit. Typical industry practice produces approximately 10,000 ppm, roughly 10 times the Stoddard limit. DoC Jet A-1's delivered specification of less than 85 ppm naphthalene, documented on the chain-of-custody Certificate of Analysis, is below the Stoddard solvent regulatory limit, a meaningful occupational health marker. A helicopter operator who switches to DoC Jet A-1 can document, from the delivery CoA, that the naphthalene content of the fuel used in its operations meets a standard more stringent than the HSE's own industrial solvent limit for the same compound.
This regulatory disparity is not scientifically defensible. Naphthalene molecules absorbed by a refuelling technician breathing jet fuel vapour are physiologically identical to those absorbed by an industrial worker using Stoddard solvent. The gap reflects a historical accident of classification: jet fuel has been regulated as a fuel product, not as a chemical substance, and has therefore been outside the scope of occupational chemicals legislation that would otherwise require carcinogen substitution. As the military helicopter litigation develops and its exposure evidence enters the public record, this anomaly is likely to attract increasing scrutiny from the HSE, the Military Aviation Authority, and the Civil Aviation Authority.
| Product / Standard | Naphthalene Content | Regulatory Framework | Worker Exposure Context |
|---|---|---|---|
| Stoddard Solvent (White Spirit) | ≤0.1% (≤1,000 ppm) | CLP / REACH / HSE COSHH, chemical safety regulation | Industrial degreasing, parts washing, dry cleaning |
| Jet A-1: DEF STAN 91-091 / ASTM D1655 Maximum | ≤3.0% (≤30,000 ppm) | Fuel specification, combustion performance rationale only | Military and civil aviation fuelling, maintenance, cabin air exposure |
| Jet A-1: Typical Industry Practice | ~7,800–11,800 ppm | No naphthalene minimisation requirement in current specification | All operational phases of helicopter operation |
| DoC Jet A-1: Delivered Specification | <85 ppm, documented on CoA | ASTM D1655 / DEF STAN 91-091, same framework, higher quality; naphthalene <85 ppm as additional CoA parameter | Same platforms, same personnel, same exposure pathways, with documented evidence of reduction |
| UK Workplace Exposure Limit (vapour) | 10 ppm (8-hr TWA) | EH40/2005, HSE occupational exposure standard | Airborne vapour concentration limit in the breathing zone |
The regulatory anomaly identified above is likely to be resolved over the coming decade by one of three pathways: (a) the HSE issuing enforcement guidance bringing aviation fuel handling formally within the scope of COSHH carcinogen controls; (b) the Military Aviation Authority or ASTM updating DEF STAN 91-091 or ASTM D1655 to include a naphthalene minimisation objective driven by occupational health rather than combustion performance; or (c) the ongoing litigation producing court findings that compel regulatory review. In each scenario, operators and manufacturers who have proactively evaluated and adopted DoC Jet A-1 will be positioned to demonstrate ALARP compliance in advance of formal regulatory change. The ALARP principle does not require regulation as a precondition of action; it requires action wherever action is reasonably practicable, regardless of whether a regulator has yet imposed it.
Three direct mandates arising from the intersection of ALARP, duty of care, and the UK military helicopter litigation
The intersection of the ALARP principle, the common law duty of care, and the evolving military helicopter litigation creates three practical mandates for helicopter OEMs operating in the UK market. These are not merely strategic recommendations; they represent the minimum evidential posture required to defend against foreseeable negligence and COSHH claims arising from crew exposure to fuel-derived carcinogens.
OEMs must formally document, in their technical records and operator communications, that their airframes and fuel systems are compatible with any fuel meeting ASTM D1655 and DEF STAN 91-091, irrespective of where within the specification that fuel sits on the aromatic content scale. This is not a new certification exercise. DoC Jet A-1 already meets ASTM D1655 and DEF STAN 91-091 in full. Every aircraft whose flight manual states "use fuel conforming to ASTM D1655 / DEF STAN 91-091" is already authorised, under its existing airworthiness certification basis, to operate on DoC Jet A-1. No new approval, type certificate amendment, or supplementary qualification is required.
What the OEM should do proactively is to make this compatibility explicit: issue a formal technical statement confirming that DoC Jet A-1, meeting ASTM D1655 and DEF STAN 91-091 with the additional naphthalene specification documented on the chain-of-custody CoA, is a compatible fuel for its platforms; and update aircraft technical manuals accordingly. This is a documentation action, not an engineering one. Its value is in creating a clear, dated, evidential record that the OEM took a positive step to enable exposure reduction, rather than passively perpetuating the status quo.
The liability protection afforded by this action is disproportionately high relative to its cost. An OEM who has issued such a statement has discharged the primary element of its duty of care in respect of fuel-derived carcinogenic exposure. An OEM who has not, and who faces litigation from a crew member with a naphthalene-attributable health condition, must instead explain why it took no action despite the availability of a certified, compatible, operationally identical lower-toxicity alternative.
Flight manuals and standard operating procedures must be reviewed and updated to explicitly document the occupational health risk associated with exhaust fume exposure during high-risk manoeuvres: sustained hover with cabin doors open, hot-loading operations, and low-level flight in confined spaces. This is not a counsel of perfection: it is the minimum documentation standard required to demonstrate that the OEM has informed operators of a known and foreseeable risk, satisfying the product safety warning obligation under common law and the Consumer Protection Act 1987.
More importantly, where DoC Jet A-1 is confirmed as compatible with the aircraft (which, as noted above, follows necessarily from ASTM D1655 / DEF STAN 91-091 compliance), operators should be actively informed of its availability and its occupational health credentials: specifically, that it delivers naphthalene below 85 ppm on every delivery's chain-of-custody Certificate of Analysis, against a typical industry standard of 7,800–11,800 ppm. The OEM who has documented a certified fuel-based exposure mitigation and communicated it to operators has substantially strengthened its liability position relative to one who has taken no action at all.
This documentation mandate serves a dual legal function: it discharges the OEM's duty to warn under product liability law, and it creates an evidential record, available in any subsequent litigation, that the OEM took proactive steps to reduce the foreseeable carcinogenic hazard rather than waiting for judicial or regulatory compulsion.
By formally confirming that DoC Jet A-1 is compatible with its platforms under the existing ASTM D1655 / DEF STAN 91-091 certification basis, and by communicating that confirmation to operators through technical manuals and operator bulletins, an OEM achieves a critically important legal outcome: the residual liability for fuel selection shifts to the operator. An operator who subsequently chooses to purchase and burn conventional high-aromatic standard Jet A-1, when a certified, compatible, lower-toxicity alternative is commercially available and has been flagged by the OEM, bears the primary liability burden for the resulting occupational exposure under COSHH Regulation 7 and employer negligence principles.
The mechanism is straightforward. The OEM discharges its duty by: (a) confirming DoC Jet A-1's compatibility under existing certification; (b) informing the operator of its availability and occupational health credentials; and (c) updating operating documentation accordingly. Thereafter, the operator is the duty-holder who must justify, under COSHH and ALARP, why the lower-toxicity certified fuel was not adopted. The litigation risk does not disappear; it is proportionately redistributed to the party who controls the purchasing decision.
For OEMs supplying aircraft to the UK military, this is particularly valuable. The MoD, as operator and employer, would bear the primary COSHH and employer liability for continued fuel selection once an OEM has made a certified lower-toxicity alternative available and documented its compatibility. The OEM's residual exposure is confined to the period before such notification, a materially more defensible position than one in which the OEM has taken no action at all.
How DoC Jet A-1 is produced, why it remains within ASTM D1655 and DEF STAN 91-091, and how its additional naphthalene specification is delivered and evidenced
DoC Jet A-1 is not produced by blending in a different additive, selecting a different crude feedstock at random, or simply accepting whatever the refinery produces within the specification band. It is produced through intentional post-processing to extract aromatics and polycyclic aromatic hydrocarbons, including naphthalene, from a standard Jet A-1 base stock. This extraction step is deliberate, targeted, and applied to achieve specific occupational health and combustion quality objectives.
The total aromatic content is reduced to approximately 8.5% by volume. This figure is not arbitrary. It represents a deliberate engineering balance: deep enough to achieve meaningful PAH and naphthalene reduction, but maintained within a range that preserves full compliance with ASTM D1655 and DEF STAN 91-091, both of which set a maximum (not minimum) aromatic limit of 25% v/v. The 8.5% level also preserves the paraffinic and cycloparaffinic fractions that provide the fuel's energy density, freeze point, and lubricity characteristics.
1: Combustion Completeness and Soot Suppression: PAHs are, by their molecular structure, significantly more resistant to complete oxidation than paraffins or naphthenes. Their aromatic ring systems require elevated combustion temperatures for full breakdown. At the partial-power hover conditions of rotary-wing operations, a proportion of PAH molecules survive the combustion zone incompletely oxidised, emerging as soot particles and unburned PAH species. These soot particles serve as nucleation sites for contrail formation. By removing the PAH precursor load before combustion, DoC Jet A-1 reduces the soot nucleation pathway at source, producing fewer and smaller combustion-derived particles and reducing the precursor availability for contrail formation, particularly at the mid-altitude cruise conditions relevant to longer-range helicopter operations.
2: Occupational Health and Naphthalene Reduction: Naphthalene, the simplest and most abundant PAH in jet fuel, is an IARC Group 2B possible human carcinogen. Its presence in standard Jet A-1 at concentrations of 7,800–11,800 ppm, while industrial solvents containing the same compound are regulated to a maximum of 1,000 ppm, represents a structural occupational health anomaly. The intentional extraction process in DoC Jet A-1 reduces naphthalene to below 85 ppm, a level that is not only compliant with ASTM D1655 and DEF STAN 91-091 but is, on the naphthalene parameter, below the limit imposed on industrial cleaning solvents under COSHH chemical safety regulation.
The two rationales are complementary. The combustion engineering rationale (fewer PAHs in the fuel means fewer soot nuclei and lower unburned PAH in the exhaust) and the occupational health rationale (lower naphthalene in the fuel means lower naphthalene vapour in the breathing zone of refuelling personnel and lower naphthalene in the combustion products recirculated into the cabin) both follow from the same physical intervention: extraction of the PAH fraction before delivery.
It is important to state clearly, because the point is sometimes misunderstood: DoC Jet A-1 is not a novel aviation fuel, a sustainable aviation fuel (SAF) blend, or a fuel seeking supplementary approval. It is Jet A-1, the same product category that has been used in gas turbine aircraft for decades, delivered at a higher standard of purity. Its compliance with ASTM D1655 and DEF STAN 91-091 is not provisional, conditional on further testing, or dependent on OEM approval. It is full, current, and unconditional. Every aircraft certified for ASTM D1655 or DEF STAN 91-091 fuel is already authorised to operate on DoC Jet A-1 under its existing airworthiness certification basis.
The comparison with SAF is instructive. SAF blends, whether HEFA, PtL, or other approved pathways, require a specific ASTM approval process (ASTM D4054 or the fast-track OEM-led pathway), confirmation of the blend ratio, and explicit OEM endorsement before use. DoC Jet A-1 requires none of this. It is already within the specification. The aromatic content of 8.5% v/v is not close to any specification minimum floor; it simply sits at a lower point within the permitted range, as do many commercial Jet A-1 supplies that happen to be derived from paraffinic-rich crude feedstocks. The difference is that in DoC Jet A-1, this lower aromatic level is intentional, consistently maintained, and documented on the delivery CoA.
As is standard industry practice for aviation turbine fuel deliveries, DoC Jet A-1 is accompanied by a full Certificate of Analysis covering the complete ASTM D1655 / DEF STAN 91-091 parameter matrix for each delivery batch: density, distillation profile, flash point, freezing point, viscosity, thermal stability (JFTOT), smoke point, acidity, copper corrosion, water reaction, lubricity, and all other required parameters.
The distinguishing feature of the DoC Jet A-1 CoA is that it includes, as an additional specification parameter, the naphthalene content of the batch, confirmed at less than 85 ppm by appropriate analytical method. This is not a future aspiration or a batch-to-batch variable: it is a delivered, measured property of every supply, included in the chain-of-custody documentation in the same way that density or flash point is included. The operator who receives DoC Jet A-1 receives, with every delivery, a document that states the naphthalene content of that batch was below 85 ppm, a figure that is, as noted above, below the Stoddard solvent industrial regulatory limit, more than 90 times lower than typical Jet A-1, and over 350 times below the Jet A-1 specification maximum.
This CoA-level documentation has direct legal value for operators seeking to demonstrate ALARP compliance. It creates a contemporaneous, batch-specific, laboratory-verified record that the fuel used in operations on a given date met a naphthalene standard far below what the specification requires; a record that, in any COSHH investigation or personal injury litigation, demonstrates that the operator took positive, documented, evidenced steps to reduce carcinogenic exposure to as low as reasonably practicable.
| Parameter | DoC Jet A-1 (Delivered) | Standard Jet A-1 (Typical) | DEF STAN 91-091 Limit | Evidence Basis |
|---|---|---|---|---|
| Total Aromatics | ~8.5% v/v | 15–20% v/v | 25.0% v/v max | TERC verified; ASTM D1319, January 2025 (SAFL-043) |
| Naphthalene (PAH) | <85 ppm, on delivery CoA | ~7,800–11,800 ppm | 30,000 ppm max | Measured and documented on chain-of-custody CoA, every delivery batch |
| Total Sulfur | <15 ppm | 400–600 ppm | 3,000 ppm max | ASTM D5453, accredited laboratory certificate per delivery |
| nvPM Mass (APU test, idle/RTL) | ~20–30% lower vs baseline | Baseline | N/A | TERC LCAF APU back-to-back test, March 2025 (available under NDA) |
| nvPM Mass (APU test, full load) | ~30–40% lower vs baseline | Baseline | N/A | TERC LCAF APU back-to-back test, March 2025 (available under NDA) |
| Expected nvPM (interpolated, 8.5% aromatics) | 30–45% reduction | Baseline | N/A | TERC "Closing the Gap" research, interpolated from 13.1% and 7.1% test fuels |
| Lubricity (HFRR, ASTM D5001) | ~350 µm WSD (superior) | ~420 µm WSD (typical) | 0.85 mm (850 µm) max | TERC verified; HFRR, ASTM D5001, January 2025 |
| Density at 15 °C | 791.4 kg/m³ | ~800 kg/m³ | 775–840 kg/m³ | TERC verified; ASTM D4052, January 2025 (SAFL-037) |
| ASTM D1655 Compliance | Full compliance | Full compliance | Required | Full specification CoA, every delivery batch, accredited laboratory |
| DEF STAN 91-091 Compliance | Full compliance | Full compliance | Required | Full specification CoA, every delivery batch, accredited laboratory |
The ALARP test requires that a risk be reduced until further reduction would be grossly disproportionate to the benefit. DoC Jet A-1 satisfies this test decisively in the rotary-wing occupational exposure context.
For a helicopter manufacturer or operator asked, in litigation or before the HSE, why personnel exposure to naphthalene and aromatic combustion products in rotary-wing operations was not reduced to ALARP levels, the answer must be more than "the fuel met the specification." The specification was designed for combustion performance, not occupational health. The ALARP question is not whether the fuel was compliant; it is whether the exposure was as low as reasonably practicable given what was available.
DoC Jet A-1 is available. It meets ASTM D1655 and DEF STAN 91-091 in full. It delivers naphthalene below 85 ppm on its chain-of-custody Certificate of Analysis, a figure documented in the same format as density and flash point, for every delivery. It requires no modification to aircraft, infrastructure, or maintenance procedures. The manufacturer or operator who has formally evaluated this fuel and documented the evaluation has addressed the ALARP duty. The one who has not, knowing that it exists, must explain the omission to a court, a tribunal, or the HSE.
Summary findings and the actions recommended for helicopter OEMs and military operators
DoC Jet A-1 represents a qualitative shift in the legal and occupational health landscape of the UK rotary-wing sector, not because it is a new category of fuel, but precisely because it is not. It is the same Jet A-1 specification, delivered at higher purity, under the same chain-of-custody framework, to the same aircraft, with no operational disruption whatsoever. It is the availability of a solution this frictionless that changes the legal calculus. The conclusions of this paper are as follows.
This white paper is produced by DM-XTech UK Ltd for informational and commercial purposes. It constitutes general commentary on the legal and regulatory landscape applicable to helicopter OEMs and operators in the United Kingdom and does not constitute legal advice. Organisations seeking to understand or address their legal obligations under ALARP, COSHH, or common law duty of care should obtain qualified legal advice specific to their circumstances. TERC data cited herein is available to qualified parties under non-disclosure agreement from DM-XTech UK Ltd.
White Paper: DoC Jet A-1, ALARP, and Duty of Care in UK Rotary-Wing Aviation
Published by DM-XTech UK Ltd | Exclusively prepared for Leonardo Helicopters UK | Commercially Sensitive
Validated by TERC, University of Sheffield | ASTM D1655 / DEF STAN 91-091 Certified
doc_jet_a-1@dm-x.us | www.dmxtech.co.uk