The Neglected Fire Vulnerability of Historic Artefacts

The preservation of immovable cultural heritage in the face of fire hazards presents a unique and critical challenge due to the irreplaceable nature of historic constructions and their contents.

Recent devastating fires in prominent heritage sites worldwide, such as the Notre Dame Cathedral in 2019 and the National Museum of Brazil in 2018, highlight the necessity of robust fire risk and vulnerability assessment methodologies specifically designed for cultural heritage. This platform published an analysis on such matter in the post titled “Why Care Fire Risk to Non-Structural Historic Elements.”

Why study specific Fire Risk Indices for Historic Buildings?

Traditional fire safety approaches often focus primarily on life safety and are generally designed for modern buildings, making them insufficient for heritage assets that combine fragile architectural elements with movable historic objects and artworks.

Existing methods tend to omit key factors such as the combustibility of movable heritage contents and the interplay between structural and non-structural fire vulnerabilities.

To address this gap, Salazar et al. (A new fire damage index to assess the vulnerability of immovable cultural heritage – 2024) propose the Potential Fire Damage Index (PFDI), an innovative indicator-based methodology that integrates twenty-one carefully selected Fire Vulnerability Indicators (FVIs) grouped into four categories:

• Properties of Built Elements,
• Utilities,
• Firefighting Measures,
• Emergency Preparedness Planning.

This comprehensive approach accounts for both immovable structural features and the movable or decorative elements that substantially contribute to fire load and damage potential.

The PDFI Scoring System

A novel aspect of the PFDI is its scoring system, which uses a “weakest link” principle within each category to ensure that critical vulnerabilities are not masked by better-performing factors.

The final weighted index provides a quantitative yet practical measure of the expected fire damage potential, independent of national fire safety codes, making it adaptable across various heritage contexts.

The methodology was demonstrated through a detailed case study of a historic church in Portugal, revealing significant fire vulnerabilities and enabling the identification of targeted mitigation measures.

The PFDI offers cultural heritage managers and fire protection professionals a valuable tool to prioritize resources, guide preservation strategies, and ultimately reduce the risk of catastrophic fire damage to historic assets.

Protecting immovable cultural heritage buildings from fire requires a comprehensive assessment of fire vulnerability that accounts not only for the structural elements of the building but also for the historic non-structural and movable objects contained within them.

These objects—such as decorative finishes, artworks, timber furnishings, textiles, and archives—are often highly vulnerable to both direct fire damage and harmful fire byproducts like smoke, heat, soot, and water from suppression efforts.

The Key Categories of PDFI

The Potential Fire Damage Index (PFDI) integrates twenty-one Fire Vulnerability Indicators (FVIs) grouped into four key categories, each reflecting critical aspects of fire risk and damage potential:

1. Properties of Built Elements (CPBE): Covers physical fire vulnerability related to the building’s construction materials, fire load—including both immovable components (walls, beams, wooden structural elements) and movable contents (artifacts, furnishings), compartmentation, vertical/horizontal fire spread potential, and conservation state.
2. Utilities (CU): Focuses on fire risk related to electrical installations, gas supply, heating and ventilation systems, and security measures like CCTV, which can facilitate both fire ignition and propagation or help mitigate risk.
3. Firefighting Measures (CFM): Evaluates available fire protection systems such as smoke control, fire detection/alarm, active suppression systems, water supply, and expected arrival time of fire rescue services.
4. Emergency Preparedness Planning (CEPP): Assesses the presence and quality of evacuation plans, emergency responses, evacuation routes, and signage, emphasizing preparedness for both occupant safety and movable asset protection.

Key Considerations about Fire Risk to Historic Artefacts

Fire load density (FVI1) comprehensively encompasses both immovable fire loads, such as structural and fixed decorative elements, and movable fire loads, including historic paintings, textiles, furniture, and archival documents. Movable heritage substantially contributes to the total fire load, thereby influencing fire development and damage potential.

In this context, several indicators specifically address the vulnerability of finishes, linings, and decorative elements that can accelerate fire spread and exacerbate damage severity.

Furthermore, in the context of emergency preparedness, appropriate measures should incorporate strategies for evacuating or safeguarding movable cultural assets alongside occupants.

Additionally, the inclusion of smoke control systems and fire detection is paramount to mitigating the detrimental effects of fire byproducts, including smoke, soot, toxic gases, and heat, which are highly damaging to delicate historic objects.

The PFDI method prioritises categories and indicators where the “weakest link” (the most underperforming indicator) determines the vulnerability score, ensuring that highly vulnerable non-structural elements appropriately influence the overall risk assessment.

Scoring and Weights

Each indicator is scored based on a “Damage Potential Class” (from A = low damage potential to E = very high damage potential). The final PFDI score is a weighted sum of the highest scores in each category, balancing structural fire risks, utility-related hazards, firefighting capabilities, and emergency planning.

This approach prevents better-performing indicators from masking critical vulnerabilities, such as fragile historic contents.

Practical Application and Validation

The PFDI was applied to a case study of a historic Portuguese church, where assessments revealed significant vulnerabilities in both its structural and movable heritage elements.

The study demonstrated how targeted mitigation measures, including improved fire detection, smoke control, electrical safety upgrades, and emergency planning focusing on movable assets, could effectively reduce fire vulnerability from severe to moderate levels.

A Focus on Finishes and Linings Indicator (FVI3)

The indicators that specifically address the vulnerability of finishes, linings, and decorative elements in the context of fire risk assessment of immovable cultural heritage are primarily found within the Properties of the Built Elements (CPBE) category of the Potential Fire Damage Index (PFDI) method. The key indicator is FVI3.

• What it covers: This indicator evaluates the combustibility, flame spread capability, and smoke production potential of the most abundant combustible materials found in the non-structural elements of the heritage construction. These include finishes and linings on surfaces such as doors, windows, ceilings, walls, and decorative elements.
• Specific considerations:
  • Distinguishes between vertical and horizontal elements/finishes/linings because vertical combustibles tend to accelerate fire spread due to upward heat and flame movement.
  • Differentiates combustible materials by their flash/ignition points (above or below 230 °C). For example, vertical finishes with low flash point materials (e.g., paper, some plastics, bamboo) represent a higher fire vulnerability.
  • Takes into account fire retardant surface coatings or finishes, which can mitigate vulnerability by reducing flame spread or ignition likelihood.
• Damage Potential Classes (DPC): The scoring ranges from low damage potential (A) when only non-combustible finishes exist, up to very high damage potential (E) when both vertical and horizontal finishes contain highly combustible materials with low ignition points.

Additional relevant aspects linked to elements vulnerability:

• Fire Load Density (FVI1): This indicator sums the fire load contributions of both the immovable built elements and the movable contents, which can include decorative objects, furnishings, artworks, textiles, and other heritage objects. The combustible nature of such finishes and decorative elements contributes to the overall fire load, thereby affecting fire severity and spread.
• Conservation State (FVI7): Assesses the condition of combustible materials including finishes and decorative elements. Materials in poor condition, with biological colonization or high porosity, are typically more vulnerable to fire damage.

Summarising

• The FVI3 (Finishes and Linings) is the main indicator explicitly addressing the vulnerability of finishes, linings, and decorative elements in cultural heritage buildings.
• FVI3 evaluates material combustibility and fire propagation potential, especially for vertical surfaces where decoration and finishes often play a key role.
• FVI3 works together with FVI1 (fire load) and FVI7 (conservation state), which also reflect the fire vulnerability related to finishes and decorative elements in broader terms.