12 C O N T E X T 1 1 3 : M A R C H 2 0 1 0 Bob Johnson Choose your extinguisher carefully The combination of a group of children, two types of fire extinguisher and a 13th century church led to a £300,000 bill for clean-up and restoration. It has been recognised for some time that correctly placed fire extinguishers, combined with staff trained in their use, are a useful first line of defence against a fire in its early stages. If used correctly, they can prevent a fire getting out of control and causing untold damage to a property. It may therefore seem strange that a fire extinguisher intended to help prevent damage can itself cause considerable harm to both buildings and their contents. An incident in a Grade I 13th century church clearly demonstrated the importance of carefully considering the suitability and positioning of dry powder extinguishers in heritage buildings. Those who have never seen a dry powder extinguisher discharged may be surprised by the quantity and spread of the powder.While hopefully putting out a fire, the discharge creates a vast cloud of particles which can take days to settle and clear up. This can result in areas such as kitchens and offices becoming temporarily unusable, food stuff being contaminated and expensive office equipment requiring replacement. What is less well known is that if the powder particles become damp they may form an acidic paste that can corrode and degrade stonework, metalwork, fabrics and other materials. In the case of the 13th century church, a group of children deliberately discharged both dry powder and water extinguishers in the church.The ‘damp’ particles from the dry powder extinguisher settled on virtually every surface throughout the building, including the organ, roof beams and stained glass. Scientific testing established that the resultant paste was corrosive, requiring all surfaces to be cleaned to avoid damage. Clean-up operations started with the extensive vacuuming of the powder discharge by professional cleaning services. Restoration of the property followed. It included conservation specialists for such areas of the historic property as the pipe work, the electrical circuits of the organ, the painted chancel ceiling, the chancel screen and the pulpit. High-level surfaces throughout the church had to be cleaned to prevent future deposition of powder on to the area below, and damage to the stonework at high level. The eventual clean-up and restoration bill for the property was £300,000. Even when discharged to tackle a fire, there is still a strong likelihood that the powder from a dry powder extinguisher will become damp and cause further damage to the property. As a result of this incident, Ecclesiastical Insurance is advising customers to review the type and location of extinguishers on their premises. Should they find that dry powder is present in areas where there are historic items or fabric, serious consideration should be given to replacing these with different extinguishers. The same considerations apply in areas with electrical equipment, such as computers, which are likely to be adversely affected by the powder. Fortunately, alternative extinguishers (such as carbon dioxide or AFFF (aqueous film forming foam) are readily available in the large majority of cases. These are potentially less hazardous in a historic environment, but will still deal effectively with a fire in its early stages. Bob Johnson is technical survey manager for Ecclesiastical Insurance.
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