OD021

1. OD021 • Prior to the 2004 IECEx meetings in Slovenia it was reported that their appeared to be a difference in interpretation of the requirements of the Intrinsically Safe Standard IEC 60079-11 Edition 4 between the different test laboratories. • At the ExTAG meetings in Slovenia in 2004 the ExTAG committee, identified the need for a guidance document for use by ExTLs and ExCBs when conducting assessments of apparatus and systems utilising the Intrinsically Safe (IS) technique of explosion protection. • ExTAG WG08 was established to produce a document for submitting to the ExTAG meetings in UK in 2005.

2. OD021 • The original WG08 team consisted of “volunteers” from Australia, Denmark France, Germany, USA and UK. • The proposed document was based on IEC 60079-11 Edition 4 not the draft version of Edition 5 as at the time the Intrinsically Safe Standard was undergoing some significant changes.

3. OD021 • At the 2005 ExTAG Buxton meetings document ExTAG/74/R was submitted for review. • This document had a six queries highlighted that WG08 requested the IS Maintenance Team feedback on. Feedback was received on several points from members of the MT and incorporated in to the document. • The original document was published in January 2006 as OD021 • The convener would once again like to thank all members of WG08 for their time and effort in producing the document within the agreed timeframe.

4. OD021 Since publication request for changes to the published OD021 came from SG31G these changes effect the following clauses of OD021; • Clause 4.2. Capacitive Evaluation • Clause 5.2. Inductive Evaluation. • Clause 7.2. Thermal Evaluation • Following these requests for changes a small group comprising of the Chairman of TC31, the convener of the IS MT and the convener of WG08 was held on 29th May 2006 following this meeting changes where made to OD021 and circulated to the individuals who requested the changes and to WG08 members for their review. • The revised document was then published as OD021V2 in July 06. • It is also noted that the UK has presented a paper of comments ExTAG-96-CC on OD021V2 and these comments have not been addressed in this presentation.

5. OD021 Clause 4.2 Capacitive Evaluation • Concern expressed over equivalent circuit shown in figure 1 • Reference to increased voltages has been replaced by reference to the relevant clause in the standard. • Clarification has been added that V1 is greater than V2. • Resistor R1 now identified in figure 1. • Review of changes to OD021V2

6. OD021 Clause 5.2 Inductive Evaluation • Concernexpressed about the additional voltage due to forward voltage drop across the diode. • This clause has been modified so it only now refers to zener diodes • Review of changes to OD021V2

7. OD021 Clause 7.2 Thermal Evaluation • The main issue with this clause was the “suitability” of the encapsulation for thermal evaluation. • The bulk of this clause has now been removed. However, it should be noted that even Edition 5 clause 6.6 is still vague on how damage to encapsulation from high temperatures should be assessed. • OD021V1 had highlighted this as an issue and was waiting for a ruling from the IS MT. • Review of changes to OD021V2

8. OD021 Clause 7.2 Thermal Evaluation • Concern over temperature evaluation on capacitors. • This has been changed to now only draw attention to conditions when electrolyte and tantalum capacitors. • Concern over temperature evaluation on hot spots of windings etc. • Reference to hot spots deleted Review of changes to OD021V2

9. Future Items • The following suggestions have been received for inclusion in the next version of OD021; • Up date required to take in to account IEC 60079-11 Edition 5.0 • Inductors used in dc – dc converters • connection of unspecified equipment to portable IS equipment in a safe area for the purposes of battery charging / downloading data / uploading data. • SIM Cards • IS Systems • Capacitor isolators?? • Any more???? • Surface temperature evaluation on surface temperature of components included in OD21.