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Understanding BS 7903:2020

Why was there a need for BS 7903:2020

With the publication of BS EN 124:1994 “Gully Tops and Manhole Tops for Vehicle and Pedestrian Areas” and the simultaneous withdrawal of its UK-dedicated predecessor BS 497, the UK market believed that there was a need to derive an advisory British-only standard which could adequately bridge the difference and perceived deficiencies between the new BS EN 124 and old BS 497.

The result was BS7903:1997 which became the advisory standard and included prescriptive information to guide UK manufacturers and specifiers alike. That same year, Highways England co-sponsored a University of Nottingham research project which provided a long-awaited scientific basis for more-effective chamber/gully top construction and design. The findings from this research project provided the foundation for derivation of subsequent Highways Agency DMRB chamber top and gully top-related advice notes such as HA 104/02 & 09.

With the release of HA104/02 (with 09 to follow) and its respected pedigree, BS 7903:1997 became generally superfluous as there were some common subject areas that the HA document addressed in a more effective way, as well as its inclusion of foundation advice.

However, BS 7903 still remained as the reference document for chamber/gully top design features such as lifting key and keyways and frame flange web/gussets, which BS EN 124 contained no provision for.

Since the release of the Highway Agency’s chamber top related documents, further WRc research crucially identified that foundation issues were the main cause of premature highway installation failure, and that these issues were strongly influenced by chamber/gully top design features and the foundation materials that were selected to operate in conjunction with them.

Further service experience of improved product design, installation materials and practice has served to identify other previously unacknowledged factors involved in premature installation failure. Narrative on this has now been provided within the latest revision of BS 7903:2020 and is just one of the reasons for its introduction.

What does BS 7903:2020 cover?

BS 7903:2020 also expands on BS EN 124 and highlights the need to consider pre-service loads (such as site construction traffic), frame designs that incorporate bedding-sympathetic features, installation materials suitability and compatibility, in-service dynamic forces imparted by traffic leading to potential seating wear, and limiting frame bearing pressure.

This 2020 Standard also removes the discrepancy that existed between the 1997 version and Highways England’s Advice Note HA104/09 in relation to frame flange dimensions where the Highways Agency took account of published research in establishing effective flange widths.

Key points BS 7903:1997 to BS 7903:2020

Subject BS 7903:1997 BS 7903:2020 How this related to products offered by Wrekin
Third party certification Refers to EN 124: 1994 requirement for third party certification, recommends the third party should be accredited by UKAS Consider the desirability of obtaining third-party certification of conformity with BS EN 124 Wrekin first to be BSI Kitemarked to BS EN 124
Classification and Place of Installation Repeats EN 124 Introduces pre-service loads e.g. construction site traffic and consideration of protection Wrekin ClickLift and Armadillo products mitigate issues from construction site traffic
Coatings Highlights that short-term coatings offer no lasting product enhancement and surface oxidization of cast iron is not detrimental Highlights that short-term coatings offer no lasting product enhancement and surface oxidization of cast iron is not detrimental  
Installation Materials No detail Says should consider workability, mechanical characteristics (e.g. compressive/tensile/flexural strength and fracture toughness), water absorption, thermal expansion and contraction, profile/shape sensitivity and chemical characteristics of bedding and packing materials. Also consider compatibility of materials Wrekin Uniform adjustment units and Unipak mortars take these factors into account
Frame Bearing Area, Pressure and Flange Width Warns against small bedding widths caused by narrow flanges. Suggests D400 150mm deep frames have minimum frame bedding width of 75mm Refers to the University of Nottingham research. Warns against small bedding widths caused by narrow flanges but no suggestion that D400 150mm deep frames have minimum frame bedding width of 75mm. Refers to University of Nottingham research. Warns against narrow flanges and cites 2.1N/mm2 maximum bedding pressure and flange width range of 50-120mm. Both through Series 500, with the latter extrapolated from its HA104/09-derived mortar specification Wrekin’s Highway and Unite products have a bearing pressure <2.1N/mm2
Lifting Provisions Where the mass of a frame exceeds 15 kg, suitable lifting holes or hooking points should be provided in the frame. These should be located to give a balanced lift. Where the mass of a frame exceeds 15 kg, suitable lifting holes or hooking points should be providedin the frame. These should be located to give a balanced lift Wrekin’s Highway and Unite products have lifting provisions
Keyways Gives dimensions Gives dimensions and introduces ‘measures to be taken to avoid key detachment during cover lifting operations should be described’ All Wrekin BS EN124 products contain patented safety keyways
Load Bearing Capacity Not mentioned In practice, excessively high loads or repeat (dynamic) loads (from, for example, sharp braking or turning) can cause permanent set (see 7.3) or flexing of a cover, leading to wear of seatings, requiring frequent maintenance or replacement of parts. BS EN 124‑1:2015 does not include a maximum value for deflection under load during this test, so specifiers might wish to seek advice from the cover manufacturer Wrekin Unite has exceptionally low deflection under load

As this over view of BS7903:2020 makes clear, it’s an important standard that assists in addressing a number of factors that previously led to installation failures which posed a safety risk as well as being a financial burden for the associated contractor and local authority. Despite the attention of most merchants and their teams understandably being captured by COVID-19, it is also a good time to get up to speed on this essential standard that benefits not only those customers across the highways industry but road users too.

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