Are you visiting from outside your region? Visit your regional site for more relevant services and pricing.

Technical questions and answersFebruary 2007

BSRIA's Librarian Stephen Loyd shares the answers to the more frequent technical enquiries from BSRIA Members.

Electrical system inspection rates

How frequently should electrical installations be inspected and tested in non-domestic buildings?

There is a table in IEE Guidance Note 3 Inspection and testing that gives recommended frequencies of inspection.

Routine checks should be made annually and are basically visual, looking for damage, deterioration, signs of overheating, missing parts, adequate labelling, and operation of switches, and test buttons on residual current devices.

The maximum period between inspections and testing is three or five years depending on building type. Recommended tests are listed in Guidance Note 3, and should be carried out by a competent person.

Refrigerant leaks and boiler air

What guidance exists on the separation of DX condensing units charged with R407c refrigerant and an adjacent gas-fired atmospheric boiler plant?

The concern in this case are the DX condensing units located in a lightwell, from which the combustion air for the boilers is being drawn. If a refrigerant gas leak occurs, then the gas could be sucked through the grille and burnt.

There does not appear to be any categorical guidance on this issue, other than the over-arching risk assessment under the Construction Design and Management (CDM) Regulations.

R407c is an entirely safe, non-toxic and non-combustible refrigerant. However, care must be taken to ensure that the units are in an area sufficiently large enough to avoid an excessive concentration of refrigerant in the unlikely event of a serious leak in the system.

This means the maximum concentration of refrigerant that can be dealt with quickly and without damage to the person. The maximum recommended system charge for R407c is 0.31 kg/m3 of room volume.

Magnetic water softeners

Do magnetic water softeners work on pipework systems?

The answer is sometimes, depending on the water chemistry.

There are two sorts of magnetic device, one using permanent magnets and the other using electromagnetic fields. Magnetic water softening devices don't soften the water as such but encourage the precipitation of scale as particles rather than as an impermeable layer on heat transfer surfaces.

Unfortunately it is not possible to predict where and when the devices will work. If a manufacturer of such a device offers one for a free trial, it may be worth a go.

Criteria for noise risk assessments

Under what circumstances do I need to conduct a noise risk assessment?

The Control of Noise at Work Regulations 2005, require a risk assessment if an employee is likely to be exposed to noise at or above 80 dB for more than six hours. If the probable noise level is 85 dB, or 90 dB, then the risk assessment will be required if the noise persists for two hours, and for 45 minutes at the higher level. The Regulations also introduce a new daily exposure limit value of 87 dB. Further information and guidance will be found in the HSE document L108 Controlling Noise at Work.

The effects of magnetic fields

What are the recommended limits of a magnetic field on people and equipment?

The potential effects of magnetic fields on equipment and people will depend on the distance from the source of the magnetic field. The magnetic strength found by BSRIA to cause jitter on computer screens is 1.3 micro Tesla, although larger screens are more susceptible than smaller screens.

For occupational exposure limits to mains frequency fields, the World Health Organisation sets a 500 micro Tesla limit. In most cases it is usually easier to move people and equipment further from the source, than to move the source itself.

The Radiation Protection Division of the Health Protection Agency can offer more advice. Telephone 01235 831600. BSRIA offers an on-site measurement and reporting for magnetic fields.

Lux to Watts per square metre

Is there a rule of thumb relationship between lux and Watts per square metre, and if a lux level is known can this be converted into Watts per square metre?

There is no direct relationship between the two as it will depend on type of lamp, its efficiency and location. Different lamps perform differently at converting power to illumination. However, the CIBSE Code for Lighting gives an average installed power density (in W/m2) for different lamp types at three lux levels in commercial and other similar applications (such as display lighting).

For more information about the benefits of BSRIA Membership contact:

Tel: +44 (0) 1344 465600
or email Membership 



A unique resource of technical and market knowledge