5 year electrical inspections – guidance for clients

We’re often carrying out audits and gap analysis surveys on behalf of our clients and one things which repeatedly creates questions is the requirement for periodic testing of the electrical supply system.

Most of us are familiar with the general requirement but few of us are clear on why and how often might be considered reasonable and so we’ve done our best to give this advice below.

Are these tests required by law?

Good question! The answer is yes and also no, they are not written into clear and specific legislation but they are related to a requirement made under the Electricity at Work Regulations (Reg 4). This requires that all electrical installations are maintained, so far as is reasonably practicable, to prevent danger.  So although no strict duty exists the inference is that you must take clear steps to ensure you comply with regulation 4, if you don’t carry out the regular tests required you can’t really show you are complying.  So the answer is that yes, you do need to carry out these inspections.

How often must I carry out these tests?

Another good question! The guidance issued in the 17th Edition of the IEE Wiring Regulations and IET Guidance Note 3 are technical guides intended for reference by electricians but we can extract some good guidance on recommended frequencies;

  • General commercial, educational establishments, hospitals, churches: every 5 years
  • Industrial premises. leisure complexes, agriculture and entertainment: every 3 years
  • Swimming pools, medical areas of healthcare premises, filling stations, caravan sites: annually

Your next steps

You don’t have to follow the above by law but you do have to show that you are doing something to comply with Regulation 4, and in practice this means doing what is described above.  If you chose not to then you must be ready to defend your actions in court should an incident occur (your insurer may also be concerned if you fail to carry out these tests).

We’d also suggest an annual visual inspection to ensure that any obvious defects are identified – consult with your electrician for more advice and if you have specific questions then contact us to some more advice.

If you’ve got questions or need support on safety in the industrial, contracting or construction sectors please contact us for sensible and proportionate advice on 01453 800100

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Please complete the form below and we promise to respond within 24 hrs. If you need more urgent help just call 01453 800109 and ask for Andrea.

Air sampling for exposure to isocyanate (MDI, TDI and similar isocyanates)

Exposure to isocyanates such as MDI, TDI or similar substances carries a very serious risk of long term health problems for skin and lungs if exposure is not properly controlled.  As occupational hygienists and qualified safety consultants we have many years experience of carrying out air sampling surveys to determine occupational exposure to many types of isocyanate used in paints, glues and foams amongst other substances.


If you would like to speak to one of our safety consultants or occupational hygienists about an air sampling survey for isocyanate exposure please contact us on 01453 800100.

ISOcyanate air sampling method

The methods closely follows the recommendations of HSE MDHS 25/3 and the principle is as follows;

A measured volume of air is drawn through a glass fibre filter impregnated with 1-(2-methoxyphenyl) piperazine mounted in a sampler and attached in the breathing zone of the exposed worker. The Methylene Di-isocyanate (MDI) is held on the filter for subsequent High Pressure Liquid Chromatography (HPLC) analysis using ultraviolet and electrochemical detection. The results of this analysis, coupled with the flow rate and time period, enable the exposure levels to be quoted as milligrams per cubic metre (mg.m-3) for application to the exposure limit published in HSE Document EH40/2001.


all (as -NCO)


8-HOUR TWA: 0.02mg.m-3

15-MINUTE REF. PERIOD: 0.07mg.m-3



Isocyanate is the functional group (-NCO) which occurs in a number of substances and their reaction mixtures. The saturated vapour concentration at 25oC varies with the substance; refer to manufacturers data sheet.

Conversion factors:

di-isocyanate 1 ppm = 3.44mg.m-3 -NCO at 25oC

isocyanate 1 ppm = 1.72mg.m-3 -NCO at 25oC

Isocyanates react rapidly with all substances having ‘available hydrogen’. This includes alcohols, amines and amide groups in proteins. Isocyanates are soluble in many organic solvents and decompose at varying rates in water. Substances carrying the isocyanate group are not detectable by smell until many times the exposure limit (for example, TDI odour threshold is about 30 times the MEL).


Organic isocyanates may arise from burning polyurethane. Only MDI is produced in the UK, by reacting methylene dianiline with phosgene in a closed process; other isocyanates are imported. About 60,000 tonnes per annum of isocyanates are used in the UK, of which about half is used for polyurethane foam, and the rest for surface coatings (paints, lacquers, inks, adhesives), foundry core binders and synthetic rubbers.


The number of persons who may be occupationally exposed to isocyanate is not known. In general, exposure can be minimised by using isocyanate prepolymers of low volatility. Control measures such as suitable extraction ventilation and use of airline breathing apparatus are needed where isocyanate aerosols or significant vapour concentrations may occur.

Exposures above 0.02 mg.m-3 isocyanate may be experienced in spray-painting large articles, with exposures briefly exceeding 0.06 mg.m-3, Respiratory protective equipment is required for these processes. In most foam plants, exposure is controlled to below 0.01 mg.m-3 isocyanate. Molten MDI can give rise to high exposures if the fume is not extracted.


Methods based on air sampling through bubbler solutions and subsequent instrumental or colorimetric analysis are detailed in MDHS 25.


The main exposure route is by inhalation of vapour, aerosol mist or dust. Isocyanate reacts rapidly with respiratory tract surfaces; its further metabolic fate is not known.


The isocyanate group (-NCO) is the functional group which causes the adverse health effect. Heavy exposure has been associated with bronchitis. There have been numerous reports on asthma due to isocyanates, but the levels which can induce sensitisation are unknown although there are anecdotal reports suggesting that peak exposures may be important. Sensitised individuals may react with severe asthmatic symptoms at very low concentrations of isocyanate, in some cases below 0.02 ppm. The development of sensitisation may occur within months of exposure, or only after years of symptom-free exposure. Sensitisation may result in the development of bronchial hyper-reactivity, and the affected individual responds to non-specific stimuli such as cold air and exercise. In these individuals, recovery may not follow cessation of exposure. Health surveillance is appropriate. {EH 16 ISOCYANATES: TOXIC HAZARDS AND PRECAUTIONS ISBN 0 11 883581 5 HSE Books (1984)}


The critical health effect of isocyanates is respiratory sensitisation and in the absence of dose-response data a no-adverse-effect level cannot be established. Consequently a maximum exposure limit was considered appropriate. This was set at 0.02 mg.m-3 (8-hour TWA) isocyanate, with a 15-minute reference period MEL set at 0.07 mg.m-3 isocyanate.