The Challenge of Choosing Fire-Extinguishing Agents in Cultural Heritage Protection

The protection of cultural heritage from fires is a complex challenge, where the speed of intervention to limit the spread of fire must be balanced with the imperative need to preserve the integrity of historic objects and structures.

This site has already discussed the topic of fire extinguishers in historic buildings in a previous post, also citing some documents of particular interest. In particular, the Research report, commissioned by the Norwegian Directorate of Cultural Heritage (Riksantikvaren) and Historic Scotland (now Historic Environment Scotland), although not recent (it was published in 2006), the Report is of great interest because it systematically addresses a crucial aspect of this challenge: the assessment of manual and automatic fire-fighting equipment in the early stages, with particular attention to their secondary effects on heritage materials.

Contrary to a simplistic view that might suggest the use of universal “special” extinguishers, the reality in historic buildings and museums is characterised by an extraordinary diversity of materials, each with its own sensitivities and reactions to fire-extinguishing agents. Paintings on canvas and board, wooden artefacts, ancient textiles (wool, cotton, linen), leather objects, metals (iron), and even mounting and support materials such as acid-free cardboard, are just a few examples of the assets that can be found simultaneously in a single museum or historical environment.

The report highlights this complexity through a series of experimental tests, in which thirteen samples of materials representative of museum artefacts were exposed not only to hot smoke, but also to different extinguishing agents. The results of these tests unequivocally demonstrate that the impact of extinguishing agents varies greatly depending on the material affected.

Chemical agents such as foam and emulsifiers showed extensive effects on surfaces, excess water caused mechanical and wetting damage, powders resulted in significant costs for post-fire cleaning and conservation and induced corrosion on metals, while the cooling effect of CO2 damaged specific materials.
This heterogeneity in material responses to fire suppression makes the selection of optimal fire-fighting equipment a non-trivial task. As the report highlights, “it is difficult to recommend a single extinguisher for all types of materials,” although some types, such as water mist devices and ABC-certified dry powder units, appear to cause the least extensive damage on some of the materials tested.

Assessing the appropriate equipment must therefore necessarily start from a thorough understanding of the specific risks of the building and, more importantly, of the materials present. This report provides essential research elements to support this critical decision-making process for safety professionals and managers, offering differentiated recommendations depending on the environments and types of cultural heritage to be protected.

Manual and Automatic Fire Fighting Equipment in Cultural Heritage Protection

This report, prepared on behalf of the Norwegian Directorate of Cultural Heritage (Riksantikvaren) and Historic Scotland, provides an in-depth analysis of fire fighting equipment and techniques available for use by museum staff in the early stages of a fire. Six categories of portable fire extinguishers, three non-extinguisher fire fighting techniques and nine small automatic fire extinguishers intended for use in museums, galleries or historic buildings were assessed. The investigation considered ease of use, extinguishing effectiveness, secondary damage (chemical, mechanical, misuse), maintenance and cost.

The research included the results of a series of tests in which thirteen representative sample materials from museum artefacts were subjected to hot smoke and six different extinguishing agents. Reference samples were compared with those exposed to smoke only and those exposed to both smoke and extinguishing methods.

Key Considerations and General Conclusions

Contrary to popular belief, museums and historic buildings do not necessarily require special extinguishers to prevent damage to cultural artefacts. Fires in these settings, as in other buildings, typically start in common objects such as electrical appliances, switchboards or waste bins, and not directly in the museum objects themselves in the early stages. Therefore, there is no significant immediate risk of extinguishing agents damaging artefacts in the early stages of the fire, when portable units are intended for use. Artefacts are typically only affected by the fire in the later stages, when portable units are less appropriate.

A key point that emerged was the prioritisation of actions in relation to the development of the fire. When firefighting actions can be initiated early and the flames are slow to develop, it is advisable to act cautiously in museum environments to preserve the artefacts. However, in buildings with a risk of rapid spread or where intervention is delayed, the priority should be direct action to extinguish the fire, rather than cautious consideration of the potential damage to the affected materials.

Impact of Extinguishing Agents on Materials

Analysis of the impact on artefacts concluded that chemical-based extinguishing agents (foam and emulsifying agents) significantly affected the surfaces of material samples. Excess water increases mechanical and wetting damage. Powdered agents incur considerable costs for subsequent cleaning and preservation and cause corrosion of iron. The cooling effect of CO2 may damage some materials.

Based on secondary damage assessments, it is difficult to recommend a single extinguisher for all types of materials. However, water mist devices and ABC certified dry units (Class A extinguishers are suitable for putting out fires that involve wood, paper, and cloth, while Class B extinguishers are better for putting out fires that involve flammable liquids. Class C extinguishers are ideal for putting out fires that involve electrical equipment) appear to cause the least extensive damage on selected materials.

Recommended Equipment for Specific Museum/Historical Environments

Recommendations for the most suitable portable equipment, based on minimal secondary damage, ability to extinguish and reduce smoke production rapidly, ease of use, cost and other factors, are as follows:

• Sensitive museum objects involved: Portable water mist extinguisher.
• Interiors of historic sites and objects: Portable water mist extinguisher.
• Furniture and paintings involved: Portable water mist or CO2 extinguisher. In galleries, for historic finishes and paintings, 10 kg AB water mist or 10 kg B CO2 portable extinguishers should be considered.
• Museum Storage: Portable water mist, CO2 or dry powder fire extinguisher. In storage, a 10kg ABC dry powder fire extinguisher is an option if items are in cases, cartons or otherwise covered.

In less vulnerable areas of museums or historic buildings, research concludes that water hoses are much preferable to hand-held extinguishers. This conclusion is consistent with the Norwegian approach, although it contradicts some current thinking in the UK. Misuse of powder extinguishers in Norway has led fire safety authorities to recommend water hoses in preference to such portable units. Managers should assess the risk of misuse on their premises and install water hoses as a first choice, with portable units for supplementary and specialist use.
In electrical installations, the application of water for extinguishing is often incorrectly discouraged due to widespread misconceptions.

Factors Determining Choice

The selection of equipment should be guided by an assessment of the specific fire risks of the site. Crucial factors in the effectiveness of use include availability, simplicity, safety, staff training and organisation. In general, portable extinguishers are more difficult to use than a water hose. Some specialty fire extinguishers require additional training. To ensure optimal tools are available and to facilitate staff familiarity, the recommended category of fire extinguishers should be chosen and mixed types should be avoided.
Damage from misuse can be significant. The risk of damage from misuse is considered to be highest with portable dry chemical or wet chemical units. Water damage is easier to manage. The risk of damage from misuse is considered to be minimal for aerosol grenades, as they would not be stored in places easily accessible to untrained personnel.

Other Techniques and Technologies

In addition to standard equipment, personnel can implement other techniques such as smothering the fire by closing doors and vents to limit the air supply, especially in small, airtight rooms.
For special conditions or as less invasive alternatives to fixed installations, tools such as water mist guns, self-piercing water mist lances, or mobile or fixed hand-operated water monitors have been evaluated. Self-piercing lances, in particular, represent an innovative technique that allows fires to be extinguished even in large rooms without risk to the operator and could make invasive fixed installations unnecessary. Water monitors are powerful tools used for external fires or to prevent spread between buildings, or to attack fires from windows or roofs. Open-air museums with wooden buildings and good water availability are typical areas for the application of fixed or portable water monitors.
In summary, the choice of manual and automatic fire-fighting equipment for the protection of cultural heritage requires careful assessment of specific risks, potential interactions with the materials of the assets, ease of use and training of personnel. Although damage from extinguishment is a concern, research suggests that assets are less at risk in the early stages of the fire, when the use of manual equipment is more appropriate