GB BPR and In-Situ Chlorine Dioxide: Precursors, Generators, Article 95 and Review Programme Status

In-situ generation in GB BPR terms

HSE defines in-situ generation as the reaction of one or more precursors to produce an active substance at the place of use, for direct application without isolation, purification, storage or transport. Chlorine dioxide is the textbook case: it is generated from precursors such as sodium chlorite (by acidification or oxidation), sodium chlorate (by reduction) or, in some systems, by electrochemical or catalytic routes, and dosed immediately. Solutions that are generated and then bottled before sale are not in-situ generation; they are ordinary biocidal products.

HSE distinguishes two situations. Where the precursors are supplied with the intention that they be used to make a biocide, the precursors are the biocidal product and the chlorine dioxide generated is the active substance. Where precursors are general chemicals not supplied for biocidal purposes, or are unmarketable (air, seawater), the chlorine dioxide generated is treated as both the active substance and the biocidal product, and the legal duty shifts to the person generating it.

Generator hardware, active substance status and product authorisation are three different things

A generator or dosing device is not a substance or mixture, so it cannot be authorised as a biocidal product under GB BPR. HSE notes that devices may nevertheless be considered as part of an in-situ product authorisation, and an authorisation may specify a particular device or the parameters it must run at. Dosing systems that only control the mixing ratio of precursors are not treated as in-situ devices. A generator's CE or UKCA marking, pressure-equipment compliance or DWI approval for use in public supply are separate matters from biocidal authorisation.

Active substance status concerns the chlorine dioxide itself, identified by the precursor route (for example 'chlorine dioxide generated from sodium chlorite by acidification'), for each product type. It can be approved, under review in the GB Review Programme, or not approved. Product authorisation concerns the specific in-situ system placed on the market: the precursors, the generation parameters, the device where relevant, and the composition of what is generated including unreacted precursor and by-products. An in-situ system can be authorised as a single product or a product family. HSE points out that the authorisation holder could be the precursor supplier, the device manufacturer or the user generating the substance, depending on the arrangement.

Article 95

GB Article 95 requires that the supplier of an active substance, or of a biocidal product containing it, appears on the GB Article 95 list for that active substance and product type. If neither supplier is listed, the product cannot be made available on the GB market at any stage of the supply chain. For in-situ chlorine dioxide, HSE gives explicit guidance using the sodium chlorite acidification route: Article 95 applies to sodium chlorite supplied with the intention that it is used to generate chlorine dioxide; it does not apply to sodium chlorite supplied as a general chemical with no such intention; and it does not apply to the acid used to perform the acidification, even where that acid is supplied for the purpose of generating chlorine dioxide.

Buyers can check the GB Article 95 list on HSE's website. Being on the list is a supply-chain requirement, not an efficacy statement and not a product authorisation.

Review Programme status and transitional arrangements

Chlorine dioxide, in its various precursor routes, is an existing active substance being evaluated in the GB Review Programme for the product types in which it was notified, which for chlorine dioxide include disinfection uses such as PT2, PT3, PT4, PT5, PT11 and PT12. While an active substance/product-type combination is under review, HSE's guidance is that a precursor supplied as a biocidal product may be supplied in GB provided the supplier complies with Article 95, advertising rules, record keeping and poison-centre notification, and with any other applicable national law. Full GB BPR product authorisation must then be applied for by the approval date of the last active substance/product-type combination in the product, in order to remain on the market.

Status can change: participants may withdraw support, HSE may redefine a substance's identity, and approval or non-approval decisions are published. Anyone relying on transitional status should check the GB list of active substances for the specific precursor route and product type rather than assuming that 'chlorine dioxide' as a whole is covered. This page describes the framework and is not a statement of any particular product's status; product-specific compliance is set out on the product's own documentation and HSE's authorised products database.

Questions to ask a supplier

Which precursor route and product types does the product rely on, and what is the current status of each on the GB list of active substances? Is the precursor supplier, or the product supplier, on the GB Article 95 list for those combinations? Is the in-situ system covered by a GB product authorisation or by transitional arrangements, and what is the applicable deadline? Does the generator's specification form part of any authorisation conditions? For public-supply drinking water, is the system on the DWI list of approved products, which is a separate regime from GB BPR?

Evidence and uncertainty

Published biofilm studies are valuable for understanding mechanisms, but their conditions may not match a particular installation. Species, surfaces, deposits and operating conditions should be recorded when interpreting evidence.

For safety-critical systems, decisions should be documented through the relevant risk assessment and management plan.

Choosing the next question

A useful next step is to identify what is known, what is inferred and what needs verification. This avoids treating a general reference as a site diagnosis.

Where a product is considered, confirm the intended use, authorisation and label directions independently of this educational guide.

Use this sequence to frame investigation and control; it is not a dosing protocol.

Expert Insights

About the Reviewer

Frequently Asked Questions

Common questions about this topic, answered by our technical team.

Related Resources

Continue exploring our knowledge base and product information.