Descriptive System Document

En 60079 part 25 Intrinsically Safe Electrical System defines the Descriptive System Document as

document in which the items of electrical apparatus, their electrical parameters and those of the interconnecting wiring are specified.

As intrinsic safety protection is a system concept each installed system must be documented to justify compliance as opposed to most other protection methods which tend to apply to individual parts of a system.
Consequently the Descriptive System Document, known as DSD, is a mandatory, document providing a record of compliance of each intrinsic safety loop/circuit. With the changes in the legal liability enforcement introduced by the 'New Legal Framework' and the 2014 Atex directive heavy fines can and are being imposed for companies that cannot produce the DSD evidence to confirm compliance.

Note. Although the legal procedure may change after 31st January 2020 as the UK leaves the EU legal system1 the requirement and possible consequences will not as the requirements are written into UK law.

The documentation can be presented in a number of ways, within the EN60079-25 Annex E examples are given for "A possible format" using a traditional drawings style although a more tabular style can be easier if generating large numbers of DSD's. Note: Using standard site installtion or circuit diagrams is rarely adequate as a DSD

Intrinsic safe systems require a (DSD) Descriptive system Document putting on record every aspect of the Intrinsic safety loops, this could be one drawing per loop or for many similar loops where but each loop must be clearly identified and contain the following information:

  • Gas Groups, Protection level, & Temperature rating
  • Cable requirements & parameters
  • Earth & bonding points
  • Justification for simple apparatus
  • Unique ID number for the DSD
  • Signed and dated by system designer

This is the responsibility of the site to have these documents.
As intrinsic safety is a system concept quite often the equipment suppliers are not in a position to create the DSD particularly if, for example supplier A provides control room equipment (barriers), supplier B the Field equipment and supplier C does the installation. Where a single supplier is supplying the complete IS system e.g. on a skid, then they may be expected to provide the DSD. However it is the sites ultimate responsibility for these documents. Where a single supplier is supplying the complete IS system e.g. on a skid, then they may be expected to provide the DSD.

(Please contact us if you require assistance with producing DSD's).


  1. The exact details of how this will be implemented are are not yet published see Brexit