BSI opens draft for Underground fire hydrants standard for public comment
Iain Hoey
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Underground fire hydrants standard draft opens for comment
A draft revision of BS 750, covering requirements for underground fire hydrants, is open for public comment until 13 April 2026.
The British Standards Institution (BSI) announced that the Draft for Public Comment is intended to support work responding to Recommendation 40 of the Grenfell Tower Inquiry Phase 2 report.
The standard is titled Underground fire hydrants. Surface box frames and covers. Specification (BS 750).
What BS 750 covers and what the amendment proposes
BS 750 specifies requirements for surface box frames and covers, including how they are designed, manufactured and tested to deliver reliable performance.
The standard is intended to provide a consistent technical framework for manufacturers, water companies and fire and rescue services, supporting durability, compatibility and effective operation.
The revised document is intended to provide greater clarity and strengthened requirements within the standard.
The proposed amendment aims to improve clarity in definitions and figures so the measurement of the flow coefficient is clearly described, in line with the Grenfell Tower Inquiry recommendation published in September 2024.
It also strengthens requirements for third-party verification and certification, alongside enhanced technical specifications designed to support greater consistency, transparency and accountability across the industry.
Consultation timetable and stakeholder engagement
The Draft for Public Comment is being promoted initially to existing users of BS 750, with wider industry engagement to follow.
Anne Hayes, Director of Sectors and Standards Development at BSI, said: “The publication of this draft reflects our clear commitment to responding constructively to the findings of the Grenfell Tower Inquiry and supporting safety across the built environment.
“We recognise the importance of actively addressing the Inquiry’s recommendations through the standards-making process.
“By progressing this amendment to BS 750, we are reinforcing our role as a responsible partner in supporting public safety and strengthening the technical standards that underpin critical fire and rescue infrastructure.”
Comments can be submitted during the consultation period via the BSI standards development site.
What underground fire hydrants are and how they work
Underground fire hydrants are fixed connections to the public water supply that allow fire and rescue services to obtain water for firefighting.
In the United Kingdom, these hydrants are installed below ground level inside a protective chamber, with access provided through a surface box and cover set into the pavement or road.
The hydrant itself is connected directly to the local water main.
It contains a valve and outlet that remain sealed until needed.
When accessed, the hydrant provides a controlled supply of water that can be directed through firefighting equipment such as hoses and pumps.
Unlike above-ground hydrants used in some countries, underground fire hydrants are not immediately visible.
Their location is marked using indicator plates, typically mounted on nearby walls or posts, which display the letter “H” and provide distance measurements to help firefighters find the exact position.
The hydrant cover at ground level is designed to protect the chamber and prevent debris or surface water from entering.
To use an underground hydrant, firefighters remove the surface cover and insert a standpipe into the hydrant outlet.
The standpipe is a portable metal pipe carried on fire appliances, which allows water to be brought above ground and provides standard hose connections.
Once the standpipe is secured, a hydrant key is used to open the valve, allowing water to flow from the water main into the standpipe and through connected hoses.
These hydrants form part of the fixed infrastructure supporting firefighting operations across towns and cities.
They provide a dependable water source in areas where fire appliances may need additional supply beyond what is carried on board.
This is especially important during large incidents, extended firefighting operations or when operating at locations distant from open water sources.
The performance of underground fire hydrants depends on several technical factors, including water pressure, flow capacity and compatibility with firefighting equipment.
Standards such as BS 750 define requirements for hydrant components, including surface box frames and covers, and establish criteria for design, manufacture and testing.
These requirements support consistency across the network and help ensure hydrants operate as expected when needed.
Water companies are typically responsible for maintaining the hydrant connection to the water main, while fire and rescue services carry out inspection and operational checks to confirm accessibility and functionality.
Regular inspection helps identify issues such as obstruction, damage or reduced flow, which could affect firefighting operations.
Underground fire hydrants are widely used across the UK because their below-ground installation protects them from accidental damage, reduces obstruction in public spaces and allows installation in dense urban environments.
Their integration with the public water supply ensures that fire and rescue services can access a distributed network of water sources, supporting firefighting capability across residential, commercial and industrial areas.