To: Directors of Environmental Health/ Chief Environmental Health Officers of London, Metropolitan, District and Unitary Authorities and Chief Executives of County Councils.

For the attention of: Environmental Services / Trading Standards / Fire Authorities / Other

This circular gives advice to local authority enforcement officers

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AUTOMATIC FLUE CLOSING DEVICES

INTRODUCTION

1 This circular includes a DATA SHEET which is intended as a working document for local authority inspectors but it may be copied to employers and other persons.

BACKGROUND

2 Paragraph 4 of the Data Sheet refers to building controls. Some building control officers may construe the fitting of an AFCD as being a breach of building control legislation.

ENFORCEMENT APPROACH

3 Occupiers and installers of gas-fired appliances should be referred to the booklet mentioned in para 3 of the Data Sheet, part of which will also be relevant to oil-fired plant. In addition, the suppliers of the gas will be able to advise on installation requirements, and also on any claims for fuel saving made by the AFCD suppliers. Occupiers should be advised to obtain and follow the advice of the manufacturer or installer on inspection and servicing.

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Health and Safety Executive	HELA Data Sheet HSE 291/8/100/9

AUTOMATIC FLUE CLOSING DEVICES (AFCD)

Introduction

1 This document contains internal guidance which has been made available to the public. The information may not be directly applicable in all circumstances and any queries should be directed to the appropriate enforcing authority.

2 An AFCD (sometimes referred to as an automatic flue damper) is a damper, usually electrically operated, which when fitted in the flue of a gas or oil-fired space or water heating appliance and connected to the appliance control system opens on firing and shuts after the main burner has been extinguished. It is claimed that energy savings can be made by retaining heat in the appliance which would otherwise be dissipated through the flue. Where appliances are operated under low-load conditions and fired only for short periods, worthwhile savings are possible.

3 Some AFCDs perform the dual function of draught control and the prevention or restriction of natural ventilation when the appliance is shut down. In 1983 British Gas Published a booklet entitled 'Automatic Flue Dampers for Use with Gas-fired Space Heating and Water Heating Appliances' which advises on the design, construction, safety and installation of AFCDs for use with gas-fired appliances

4 Occupiers who have installed, or who may be about to install, an AFCD should consult the building control authority for advice on compliance with building control legislation.

Hazards

5 Some AFCDs incorporate suitable interlocks but in the absence of adequate safeguards the following hazards may arise:

(1) where the valve is not opened before start-up any accumulated gas or oil vapour within the appliance will remain and could explode when the pilot or main burner is lit;

(2) should the valve fail to open when the burner is lit (or suffer an uncovenanted closure while the burner is alight) incomplete combustion may occur which could give rise to an explosion or toxic risk; and

(3) on equipment with a permanent pilot the damper may restrict ventilation and cause incomplete combustion (see (2) above).

Precautions

6 Whether installed on gas or oil-fired equipment AFCDs should:

(1) be so constructed that the damper remains securely attached to its spindle in all foreseeable circumstances and be resistant to the corrosive effects of products of combustion which can be particularly severe in the case of oil firing;

(2) in the case of dampers intended solely to prevent natural ventilation while the appliance is shut down, operate only to provide a fully open position and single closed position;

(3) be so installed that disconnection of any drive linkage or lever arm fitted between the drive mechanism and the damper will either cause the damper to open fully or prevent start-up of the burner;

(4) be fitted with an interlock to ensure that the damper blade is in the fully open position before initiation of the ignition sequence. The interlock should be operated mechanically by the damper spindle;

(5) Where the damper performs the function of draught control, be fitted with an additional interlock at a pre-set minimum open position to ensure that the damper is at or beyond that position during main flame operation;

(6) be provided with a safe-start check facility to prove that interlocks are in the correct position before the damper is opened;

(7) have interlocks arranged so as to operate all safety shut-off valves in the fuel supply train except those controlling the pilot fuel supply (where a permanent pilot is provided). Failure to prove that the damper is in the open position during operation should close the safety shut-off valves and, in the case of automatic burners, cause the control system to lock out. The burner control system should incorporate a time delay to prevent both the opening of the safety shut-off valves and the operation of the ignitor until the combustion chamber, passages and flues have been adequately purged. It is also desirable that the damper should remain open for a short period after firing to allow corrosive combustion products to be removed from the flue;

(8) be provided with a by-pass when fitted to an appliance with permanent pilots. This may be achieved by cutting away part of the damper blade, the area cut away being related to the size of the pilot and the amount of natural draught. Advice on this should be sought from the supplier; and

(9) be regularly serviced by a competent person.

In forced draught equipment these requirements are in addition to, not in substitution for, the normal requirement that air flow should be monitored and interlocked with the burner controls.

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