Safety alert to operators of COMAH oil/fuel storage sites and others storing hazardous substances in large tanks

Health and Safety Executive - Safety alert

Department Name:
Hazardous Installations Directorate (Chemical Industries Division)

Bulletin No:
HID 6-2010

Issue Date:
30 June 2010

Target Audience:
Chemical and petrochemical processing; Storage and distribution.

Key Issues:
This safety alert is primarily for the attention of those companies operating oil/fuel storage in large tanks and may be relevant to other sites storing hazardous substances in large tanks.


The following safety alert is primarily for the attention of those companies operating oil/fuel storage facilities. However, it may also be relevant to other sites storing hazardous substances in large tanks where level gauges are used.


The investigation into the fire and explosion at the Buncefield oil terminal depot on 11 December 2005 is continuing. Enquiries into the workings of the high level safety system to prevent tank overfill have indicated that certain aspects of its installation and testing are critical in ensuring that it works properly. Operators of similar establishments are therefore advised to carry out immediate checks where TAV level switches1 manufactured by Cynergy3 Components Limited and supplied by them, their predecessor companies2, or others, are fitted to their storage tanks.

Operators should check TAV level switches fitted with change over (double throw) reed switches. These switches are normally used in 'de-energise' mode to maintain alarm/trip circuits in 'normal' status.

Amendment June 2010

'Since HSE published the guidance in this safety alert, we have identified that it should also apply to some TAV switches with single pole, single throw (SPST) reed switches, depending on the magnet configuration. The corrective action for these switches is the same as for double throw switches. Operators should check with their suppliers for further information about relevant model types and numbers.'

The switches are tested by using a lever or plate fitted to the head of the switch, which can be raised to simulate a high level of liquid in the tank. If the switch is working, then alarms and trips connected to the switch should operate.

However, it is critical that after carrying out this test that the lever or plate is returned to the correct position and locked into place, using a special padlock supplied by the manufacturer3, and in accordance with the manufacturers instructions. Failure to do this can lead to the switch being inoperative in normal operating mode even though it gives the appearance of functioning normally when tested.

There are a number of this type of switch fitted at tank installations in GB and worldwide. HSE has taken urgent action to bring these details to the attention of operators of similar sites through relevant industry bodies across GB, Europe, the USA, and Canada.

Action required

Operators should check immediately whether they have such switches fitted, and if so:

  • ensure they have all relevant manufacturer's information concerning installation and testing and maintenance;
  • ensure they have records of correct installation, testing and maintenance;
  • ensure they are currently installed in accordance with the manufacturer's instructions, with the locking device properly fitted; and
  • complete these checks as soon as possible. [See checklist]

Where operators cannot confirm that the switches are working correctly, then other temporary measures may be adopted, until the defects can be remedied, to ensure safe operations. For example, close supervision and dipping.

The manufacturer/supplier will be contacting known users and installers of these switches to alert them to this issue and will be providing revised instructions on the safe use, setting, cleaning and maintenance of these switches. HSE has served Improvement Notices on Cynergy3 Components Limited requiring it to carry out this work.

4 July 2006

Relevant legal documents



  1. (A). F150, F160, F171, 155, 156, 157, 170 (May 1987 - December 1996). (B).14-, B17-, F15-, F16-, S14-, S17- (December 1996 - 2006). This prefix should be readily identifiable on the manufacturer's label fitted to the device eg F150 or F16-123-123 etc. Back to reference of footnote 1
  2. Crydom Magnetics Ltd, TAV Engineering. Back to reference of footnote 2
  3. As an interim measure for Type A switches a suitable padlock or fixing device or for type B switches a 5mm pin secured by a padlock or chain can be used whilst awaiting the manufacturer's equipment. Back to reference of footnote 3

General note

Please pass this information to a colleague who may have this Product/ Equipment or operate this type of system/process.

Further information

Any queries relating to the safety alert should be addressed to:
Health and Safety Executive
Hazardous Installations Directorate
Chemical Industry Division
Redgrave Court
Merton Road
Bootle, Merseyside, L20 7HS

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