Isolation and burner supervision

GAS FIRE SPECIAL ATMOSPHERE FURNACES: Isolation and burner supervision

OC 647/11

This 2-part OC provides guidance on safe isolation and burner supervision in special atmosphere furnaces, specifically furnaces lacking flame-failure devices. The Information Document (ID) may be copied and given to interested parties outside the HSE.


1 A major explosion occurred in 2002 during maintenance work on an Ipsen Abar T7 sealed-quench special-atmosphere furnace. It is understood that this type of furnace is relatively widespread in the UK.

2 HSE's investigation into the explosion revealed:

  • the need for improvements in gas isolation and flame supervision (3 out of 5 valves were found to be leaking and no flame-failure devices were fitted); and
  • a lack of understanding amongst operating companies about the standards required for second-hand furnaces.

3 The incident demonstrated the dependence of older equipment on operator experience and procedural controls to prevent explosions. By comparison, modern Standards have improved physical safeguards fitted to furnaces of this type, for example the requirement for fitting flame-failure devices.

4 As part of the actions arising out of this incident the company prepared a detailed costing for upgrading the existing furnace to the latest standards of burner safety control and supervision. This exceeded 10,000 per furnace (more than the replacement cost for a second-hand furnace) and would be unsustainable for many heat treatment companies. Given the low incident frequency, but taking account of potentially severe consequences, the view of the Specialist Inspector at the time was that upgrading to the latest standards was not reasonably practicable.

5 Subsequently, the Dangerous Substances and Explosive Atmospheres Regulations 2002 (DSEAR) now require a hierarchy of control measures. For example, under DSEAR Reg. 6, the fitting of physical control measures such as flame-failure devices must take precedence over 'software' solutions like supervision. In addition, the Institution of Gas Engineers and Managers (IGEM) published IGE/UP/12. "Application of burners and controls for gas fired process plant including furnace ovens, boilers, air heaters, etc. ", which gives specific guidance that came fully into force in March 2006.

6 The Information Document (ID) sets out the standards to reduce the risk of explosions for older equipment and for machinery supplied second-hand. This includes specifically the fitting of flame-failure devices to all second-hand equipment and retrospective fitting to existing installations where this is reasonably practicable. Where companies argue that physical improvements are not reasonably practicable they will be asked to provide justification by means of detailed risk assessment.

Date first issued: 15/01/2007

Is this page useful?

Updated 2020-12-14