Introduction & Background
The transfer of infection, including Legionella Bacteria, and/or unpleasant odours may occur in situations where the contaminated bleeds from an air handling plant discharges to a waste water drain which also receives, without an adequate water seal trap and air break, the discharge from drip trays in the air conditioning plant. The integrity of water seals provided by traps manufactured in Borosilicate Glass is a key factor in the prevention of the dissemination of contaminated air.
Product Efficiency
The transparency of Glass and its ability to perform safely with temperature and biocidal fluctuation enable the person responsible for maintaining the system to have visual access into the drains, ensuring that the colonisation of the system by sediments consisting of sludge, scale, rust and algae are prevented from providing the nutrients known to encourage the proliferation of Legionella.
The Law
Employers are required to safeguard the health of their employees at work and to ensure that other people are not endangered by the work activity (Health and Safety at Work HSW Act 1974).
The ‘Occupiers’ Liability Act 1957 – with respect to persons on the premises and common law as to negligence and nuisance with respect to those in the vicinity.
Health and Safety Commission Consultative Document of November 1989 – The Control of Legionellosis Proposals for Statutory Action’.
Recommendations
1st and 2nd reports of the committee of enquiry chaired by Sir John Badenoch into the outbreak of Legionnaires Disease in Stafford. CH I 3 PARA 283 and 284. Drains from air conditioning plants should feature glass traps to comply with HH (HAZARD) 85/6 dated 9/7/85 clause 5.
The Chartered Institute of Building Services Engineers have within T.M. 13 recommended that the application of the glass trap to A/H plant should be considered in all sensitive buildings.
The Department of Health Code of Practice for the Control of Legionella in Health Care Premises Part 5 issued July 1988.
Typical Specification
To achieve maximum isolation and seal integrity borosilicate glass trap with access tees for filling, dosing and cleaning shall be connected directly to the unit drain outlet. The trap seal shall be, wherever possible, calculated to withstand at least twice the static pressure exerted by the system fan. To further isolate the air-handling unit from contamination, it is recommended that the drainage from the unit trap also be installed in borosilicate glass to ensure a sterile condition not available to other opaque pipe materials which are easily colonised by bacteria. The borosilicate glass drain should then discharge via an air break of at least 100mm into a tundish or floor gulley/channel trapped in borosilicate glass with a seal capable of withstanding pressures exerted by the drainage system to which it is connected. Designers, manufacturers and contractors should ensure that adequate clearance has been given to allow the positioning of traps thus enabling the correct gradients of drainage to be achieved.
Maintenance
It is essential that the trap assemblies are dosed regularly with a Biocide via the access caps provided.
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