Registration requires the submission of relevant and available data on intrinsic properties of substances and exposure scenarios and, when not available, the generation of data including testing. Specific mechanisms and procedures have been introduced in REACH to enable companies to share existing data before submitting a registration: the data sharing and the joint submission. They are aimed at increasing the efficiency of the registration system and reducing costs and testing. Data sharing is obligatory for studies involving tests on vertebrate animals. As a general rule, REACH requires the sharing of information on the basis of a cost compensation mechanism.

The regulation sets out different procedures for registration and data sharing of “phase-in substances”1 and “non-phase-in substances”2.

Data sharing rules for phase-in substances

A system is established to help potential registrants find others with whom they can share data and costs: the pre-registration and the Substance Information Exchange Fora (SIEFs).
Manufacturers or importers3 of phase-in substances may benefit from extended registration deadlines if they “pre-register” their substances, i.e. if they submit a specific brief set of information to the European Chemicals Agency (ECHA) between 1 June 2008 and 1 December 2008. By 1 January 2009, a list of all pre-registered substances will be published on ECHA's website, together with the first envisaged registration deadline.
In a first step, pre-registrants of substances with the same identifiers in the list of pre-registered substances will have to establish whether their substances are indeed the same for the purpose of SIEF formation. REACH provides for the formation of SIEFs to share data among manufacturers and importers of pre-registered phase-in substances, phase-in substances registered without pre-registration4, holders of information on phase-in substances that are used as plant protection products and biocides. REACH also allows downstream users and other stakeholders (data holders) who have, and are willing to share, relevant information, to sell it to potential registrants. Manufacturers and importers may appoint a “Third Party Representative” to remain anonymous towards the other stakeholders.
A SIEF is not a legal entity or a consortium, but a forum to share data and other information on a given substance.
All SIEF participants shall react to requests for information from other participants and provide other participants with existing studies upon request. Potential registrants shall request missing information from other SIEF participants, collectively identify needs for further studies to comply with registration requirements, make arrangements to perform the identified studies and agree on classification and labelling where there is a difference between potential registrants. They may request missing information from other SIEFs if they consider their substance similar enough to the substances of these other SIEFs.
REACH gives potential registrants flexibility to decide how they organize their sharing data. For more information, see diagrams Data sharing for phase-in substances, individual and collective routes.

Data sharing rules for non-phase-in substances and not pre-registered phase-in substances

The process in place to initiate the data sharing for these substances is generally referred to as the “inquiry process”. It is essentially a three-step process whereby:

• the potential registrant must ask ECHA prior to registration if the same substance has already been registered;
• ECHA facilitates contact between the previous registrant(s) and the potential registrant(s) and/or other potential registrants, if any;
• data sharing is organized between previous registrant(s) and/or potential registrants including for new tests to be potentially conducted.
• For more information, see diagram Inquiry process.

One of the main differences with the rules for phase-in substances is the early involvement of ECHA and its role in determining substance equivalence before facilitating contacts between registrants.

Joint submission of data

REACH registrants are required to jointly submit information on the hazardous properties of the substance (studies and proposals for testing) and its classification and labelling and can, if they agree, also jointly submit the Chemical Safety Report (for substances ≥10 tonnes per year per registrant) and/or the guidance on safe use (Data to be submitted jointly or separately for registration under REACH). However, registrants are allowed to opt out from the joint submission under specific conditions (disproportionate costs, protection of confidential business information, disagreement on the selection of information with the registrant who leads the joint submission). The opting out can be partial. The right to opt out does not apply to the data sharing obligations or to the membership of the SIEF. Any exercise of opting out must be fully justified.

1. Phase-in substances: substances already manufactured or imported, under certain conditions, before the entry into force of REACH on 1 June 2007.
2. Non-phase-in substances: substances that do not meet the definition of phase-in substances as given in the regulation.
3. Non-EU manufacturers may appoint “Only Representatives” to fulfil the obligations of importers. Only Representatives are natural or legal persons established in the European Union and having sufficient background in the practical handling of substances and the information related to them. When an Only Representative is appointed, the non-EU manufacturer has the obligation to inform the importer(s) within the same supply chain of the appointment. Following such communication, the Only Representative takes up the role of the EU importers and fulfils their registration obligations.
4. Potential registrants of phase-in substances that decide to register without pre-registration are mandatory participants of the relevant SIEF once they have registered. They have the obligation to share data they hold on request. Before registration, they are subject to the “inquiry process” which applies to non-phase-in substances. Potential registrants of such substances must stop manufacture or import of their substance, after 31 May 2008, before making their inquiry.