Water Mist in Historic Heritage. Pros and Cons

Fireriskheritage.net has already covered the use of water mist systems in historic and heritage buildings. The recent reopening of Notre Dame de Paris has shown the fire safety consultants’ choice to install a water mist system to protect the “Forest“. The Forest was (and is now) the complex wooden structure of the roof, that needed more than 1.000 oaks to be rebuilt and is now protected by a water mist system.

In this regard, a brief summary of the pros and cons of using these powerful but complex systems may be useful.

Water mist fire protection systems have several advantages specific to historic buildings, focusing on minimizing damage and preserving structural integrity. Here are the key benefits:

Reduced Water Damage

• Water mist systems use up to 85% less water than traditional sprinkler systems. This significant reduction in water consumption translates into decreased water damage in the event of a fire. Protecting delicate furnishings, artwork and architectural elements within historic buildings is a top priority, and water mist systems offer an approach that minimizes the risk of collateral water damage.
• Water mist systems are particularly suited to protecting areas such as libraries, archives, historic buildings and museums, where the preservation of sensitive materials is critical. Studies have shown that water mist systems can control damage to sensitive objects, using only 30% of the water required by a traditional sprinkler system.

Greater design flexibility and discreet integration

• “Smart” design: The customizable nature of water mist systems allows for more discreet integration into historic buildings. Unlike sprinkler systems that often require bulky piping and visible infrastructure, water mist systems can be designed with smaller piping and compact components, minimizing visual impact on historic aesthetics.
• Adaptability to complex spaces: Water mist systems can be adapted to complex and obstructed spaces common in historic buildings, providing effective protection where traditional systems may be inadequate. Their ability to reach shielded areas by dispersing fine droplets makes them ideal for protecting structures with high ceilings, exposed beams and other architectural elements that may impede traditional sprinkler systems.
• Retrofit Installations: Water mist systems are suitable for retrofit installations in historic buildings where structural changes must be kept to a minimum. Compact components and design flexibility allow for easier integration with existing systems and reduce the need for invasive work that could compromise the structural integrity of the historic building.

Long-Term Preservation and Maintenance

• Although there are still concerns about the long-term maintenance of water mist systems, especially regarding the potential for corrosion, experience shows that systems with stainless steel piping remain in good condition even after 15 years of operation.
• Water mist systems require regular maintenance similar to traditional sprinkler systems, including inspection, testing and periodic replacement of stored water. A commitment to proper maintenance can mitigate corrosion risks and ensure the long-term operation of the system in a historic building.
• Efficient testing procedures: Limited water discharge during water mist system testing minimizes disruption and potential damage to protected areas in historic buildings.

Things to consider

Water mist fire protection systems present several challenges, especially when it comes to historic structures. While they offer advantages such as lower water consumption and greater design flexibility compared to traditional systems, their unique characteristics raise some concerns in sensitive contexts such as historic buildings:

• Corrosion Potential: Water mist systems rely on high-pressure nozzles with small orifices to generate fine droplets. This, combined with potential corrosive products within the piping, can lead to clogs and blockages. In historic structures, where piping systems may be older and susceptible to corrosion, this risk is amplified.
• Maintenance and Inspection: While maintenance of water mist systems is comparable to that of traditional sprinkler systems, long-term maintenance data is still limited. The lack of a solid historical knowledge base on the effectiveness and long-term maintenance of these systems in historic buildings can make it difficult to manage them and assess potential risks.
• Design Complexity: Designing a water mist system for a historic structure requires careful consideration of multiple factors such as ceiling height, shaft size, ventilation, construction materials, and type of fire load. The complexity of these calculations and the lack of a standardized design approach make the design process more onerous and potentially more expensive.
• Limited Historical Documentation: Approval of water mist systems for sensitive applications such as historic buildings is often hampered by the lack of a solid historical data base on their effectiveness and safety in real fires. The lack of empirical evidence and precedent can lead to a reluctance by approval authorities to grant permission for installation in historic settings.
• Cost: Water mist systems tend to be more expensive than traditional sprinkler systems due to their complexity and specialized components. The additional cost could be a significant barrier to implementation in historic structures, especially if preservation funding is limited.

In conclusion: when fire risk analysis suggests to install water mist?

The choice to install a water mist fire protection system in a historic structure requires a careful assessment of the potential benefits and drawbacks. The complexity of the system, the limited historical documentation and the additional costs require a careful analysis of the specific context and close collaboration with experts in fire safety and conservation. It is essential to carefully consider all the critical aspects and evaluate whether the benefits outweigh the potential challenges before proceeding with the installation of a water mist system in a historic building.

Risk analysis may recommend the use of water mist fire suppression systems over less expensive systems in a number of situations, particularly when the benefits in terms of damage reduction and environmental impact outweigh the higher initial costs, like the most of historic buildings and sites of high cultural value.

In these contexts, the minimisation of damage caused by water is of primary importance. Water mist systems, thanks to their significantly reduced water consumption (up to 85% less than traditional systems), offer effective protection while minimising collateral damage to the building and its contents. Conservation of delicate artefacts, works of art and architectural elements justifies the investment in a more expensive but less invasive system.

In summary, the risk analysis may lead to recommending the use of water mist systems when the protection of high-value buildings or artefacts, minimization of collateral damage, design flexibility and environmental impact are priorities over initial costs.