Sirius Fire Safety Consultants FAQ
Fire Engineering
What is Fire?
What is Fire Engineering?
Who is classed as a fire engineer?
What is the aim of fire safety engineering?
When should the design team be talking to a fire engineer?
What role does a fire engineer play in the design team?
In the Approved Document B (ADB) are the travel distances compulsory?
In residential units can I have an open plan configuration within the units?
My development is under 18m do I have to provide perimeter access for the fire service?
Building structure
Are there any case histories of fire-damaged buildings?
Does steel lose its ductility after being in a fire?
What compartment construction materials have been used in the tests?
Is it possible to determine how long the fire was burning?
What fire tests have been carried out?
What temperatures have been achieved in fire tests?
What compartment construction materials have been used in the tests?
Have any tests been carried out using plastics and furniture?
How does temperature affect steel strength?
Does the manufacturing route for steel affect its elevated temperature strength?
How do old structural steels behave compared with modern grades?
Is there a difference between composite and non-composite design?
What are the different types of fire protection?
Which fire protection systems are best for internal or external environments?
Are test results in the UK the same as you might expect in the USA?
What is the effect of fire on other materials e.g. masonry, concrete, wood?
Fire Risk Assessment
How can you prepare for the changes in workplace fire legislation?
What does a fire risk assessment cover?
Why is a good fire risk assessment important?
So, what do you need to carry out a fire risk assessment?
Who is a 'Competent Person'?
Why should you use an external, qualified fire risk assessor?
Q.
What is Fire?
A.
Fire is a self-sustaining oxidation process accompanied by heat and light in the form of a glow or flames. It is commonly used to describe either a fuel in a state of combustion (e.g., a campfire, or a lit fireplace or stove) or a violent, destructive and uncontrolled burning (e.g., in buildings or a wildfire). The discovery of making fire is considered one of the most important elements in the progression of humankind, for it let higher hominids ward off wild animals, cook food and provide warmth
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Q.
What is Fire Engineering?
A.
Fire Engineering is the application of scientific and engineering principles, rules [Codes], and expert judgement, based on an understanding of the phenomena and effects of fire and of the reaction and behaviour of people to fire, to protect people, property and the environment from the destructive effects of fire.
Fire Engineering includes such activities as:
The assessment of the hazards and risks of fire and its effects;
The mitigation of potential fire damage by proper design, construction, arrangement, and use of buildings, materials, structures, industrial processes, transportation systems and similar;
The appropriate level of evaluation for the optimum preventive and protective measures necessary to limit the consequences of fire;
The design, installation, maintenance and/or development of fire detection, fire suppression, fire control and fire related communication systems and equipment;
The direction and control of appropriate equipment and manpower in the strategy and function of fire fighting and rescue operations;
Post-fire investigation and analysis, evaluation and feedback.
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Q.
Who is classed as a fire engineer?
A.
A fire engineer, by education, training and experience: understands The nature and characteristics of fire, and The mechanisms of fire spread and the control of fire and the associated products of combustion, Understands how fires originate, Spread within and outside buildings/structures can be detected, controlled, and/or extinguished, Is able to anticipate the behaviour of materials, structures, machines, apparatus, and processes as related to the protection of life, property and the environment from fire, Has an understanding of the interactions and integration of fire safety systems and all other systems in buildings, industrial structures and similar facilities is able to make use of all of the above and any other required knowledge to undertake the practice of fire engineering.
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Q.
What is the aim of fire safety engineering?
A.
Fire safety engineering is concerned with minimising the impact of fire on life, safety and property and has several key objectives:
Its aims are to:
Ensure that people are able to leave a building or structure in a reasonable amount of time or go to a place of safety that will protect them from the effects of heat, smoke and structural failure.
Protect personnel in fire fighting operations in order to seek and rescue members of the public and contain the fire from spreading to neighbouring property.
Reduce the impact of fire on property and the environment
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Q.
When should the design team be talking to a fire engineer?
A.
The design team should aim to get a fire engineer involved in a project at the initial stages of the design process. A fire engineer may have a limited involvement at the early stages, but their experience may ensure that the design is right the first time and that building costs are reduced.
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Q.
What role does a fire engineer play in the design team?
A.
The fire engineer will be able to provide on going adhoc support in all fire related issues regarding the design, liase with Building Control Officers, Fire officers and the insurers to achieve a fully compliant building regarding fire safety.
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Q.
In the Approved Document B (ADB) are the travel distances compulsory?
A.
Travel distances are based upon a combination of experience and best practice and represent the maximum distance a person can reasonably be expected to walk in order to escape from a fire. Although it could not be said that a slightly greater distance would be so unsafe if designing in accordance with the guidance document ADB, designers should aim to keep travel distances as short as possible, rather than designing to the maximum distance as recommended in the prescriptive guidance. However using a fire engineer could provide justification to extend these.
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Q.
In residential units can I have an open plan configuration within the units?
A.
The travel distance dictates the answer to this; however by using a fire engineer, justification could be given to the increase in travel distances, as well as an open plan configuration within the unit.
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Q.
My development is under 18m do I have to provide perimeter access for the fire service?
A.
Strictly the answer to this is Yes, however if a fire engineer is employed, the answer to this will be dictated by the fire strategy. Often a fire engineer will be able to offset this requirement against an already installed active fire protection system.
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Building structure
Q.
Are there any case histories of fire-damaged buildings?
A.
Sirius Fire Safety Consultants are regularly appointed to advise upon the reinstatement/re-use of steel structures and buildings involved in fire and carry out both on-site checks and laboratory investigations. Its staff work closely with engineers and architects on behalf of the insurance company or building owner. However most of the projects are client confidential but several examples are included on the web site. The publication ‘The reinstatement of steel and iron framed structures’ can be obtained from Sirius Fire Safety Consultants directly. This publication also includes the fundamental research that has been carried out by staff within Sirius Fire Safety Consultants to enable scientifically based decisions to be made on the re-use /repair of steel members and components exposed to fire and smoke damage.
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Q.
Does steel lose its ductility after being in a fire?
A.
In general the ductility of structural steel is not significantly impaired when it has been heated in a fire. For some types of products such as work hardened reinforcing steel the ductility is often improved during heating but the temperatures at which this happens will usually cause a permanent loss in strength.
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Q.
What compartment construction materials have been used in the tests?
A.
Most of the common types of building materials have been used and have included:
• Dense concrete slabs
• Composite steel and concrete floors
• Blockwork walls, Plasterboard walls
• Sand on the floor.
• Some highly insulating materials have also been used such as insulating firebrick and ceramic fibre blanket.
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Q.
Is it possible to determine how long the fire was burning?
A.
There are indicators that can be used to determine the temperatures attained and the duration of heating but it is difficult to separate the two. Timber typically chars at around 0.6 to 1.0 mm per minute and therefore if the surface layers have been burnt we know that high temperatures have been sustained for only a few minutes. The thickness of char can therefore be used as an indicator for the burning period. Other factors worth noting are:
• Glass softens at around 600°C depending upon the type.
• Aluminium melts at 600°C.
Galvanised coatings would have melted by the time the temperature attains 450°C and surface degradation occurs at a temperature rise of only 200°C.
Some concretes undergo colour changes at certain temperatures (300°C and 600°C) but these are difficult to assess.
Some steel components can be used to determine the actual temperatures achieved. For example, staff within Sirius Fire Safety have developed a technique for assessing the retained strength of heat-treated bolts that is directly and quite precisely related to the temperature attained during the fire. In some cases temperatures as accurately as ±15°C can be established at the connections. Further information on the behaviour of bolts in fire is given in the research publication ‘ The behaviour of bolts at elevated temperatures’ available from Sirius Fire Safety Consultants
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Q.
What fire tests have been carried out?
A.
During the last 20 years a number of research establishments and private companies have conducted major fire tests in buildings. These include BHP in Australia, CTICM in France and The American Iron and Steel Institute in USA. In the UK, Sirius Fire Safety Consultants (the staff of which was formerly members of Corus UK (British Steel)) have been the main drivers of the fire tests conducted on steel frames and have established an International reputation in the groundbreaking research carried out. These tests had been funded jointly with the UK Government and the European Coal & Steel Community and led by Sirius Fire Safety Consultants’ research staff. The main programmes included 20 tests conducted between 1983 and 1986, 9 tests conducted in 1993 and 4 tests in 1994/5 conducted on the 8-storey steel frame at Cardington. The data is available through Sirius Fire Safety Consultants for other researchers to carry out further numerical modelling studies.
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Q.
What temperatures have been achieved in fire tests?
A.
The temperatures attained within the compartments vary according to the construction materials, type and amount of fuel load as well as the ventilation characteristics. Temperatures attained by the atmosphere when wooden cribs are burning are usually around 1000°C although this can be as high as 1200°C with compartments constructed using insulating materials. When plastics are involved in a fire such as those found in modern day offices, atmospheric temperatures easily achieve 1200°C. With regard to steel temperatures, these depend upon the size of the member but for typical unprotected beams and columns these would lag behind the compartment temperatures by around 100°C to 200°C.
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Q.
What compartment construction materials have been used in the tests?
A.
Most of the common types of building materials have been used and have included:
• Dense concrete slabs
• Composite steel and concrete floors
• Blockwork walls
• Plasterboard walls
• Sand on the floor
Some highly insulating materials have also been used such as insulating firebrick and ceramic fibre blanket.
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Q.
Have any tests been carried out using plastics and furniture?
A.
Yes, in the test programme carried out in 1983–86, plastic in the form of polypropylene sticks were often inserted into the wooden cribs and these made up 15% of the total fire load. In a test carried out on the 8-storey steel frame at Cardington the compartment was fitted out as a modern office with items such as soft furnishings, computers etc. In total approximately 20% of the fire load was made up of plastic materials.
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Q.
How does temperature affect steel strength?
A.
For hot rolled structural steel the yield strength reduces as the temperature increases dropping to about 60% of its ambient temperature strength at around 400°C and approximately 10% at 800°C. However the stress at 2% strain (normally reached when a steel floor beam attains its permitted limit of deflection) initially increases with increasing temperature reaching a peak value at around 250°C. The reason for this can be explained using metallurgical theory and involves a combination of work hardening and dynamic strain ageing.
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Q.
Does the manufacturing route for steel affect its elevated temperature strength?
A.
Yes. Any process that raises the strength of steel by a mechanical or heat treatment process will result in a greater loss in strength in proportion to hot rolled structural steels. For example, reinforcing steel achieves much of its strength by cold working at ambient temperature. Under fire conditions stress relieving occurs at temperatures above 400°C, which results in a more rapid loss in strength.
High strength bolts (Strength grades 8.8 and 10.9) achieve much of their strength by a quench and temper process. Bolts are quenched from around 850°C and this creates an extremely hard but brittle structure. They are then subsequently tempered between 475°C to 600°C to restore some ductility but with a measured loss in strength. If these temperatures are then exceeded during a fire the bolts over temper with a resulting sharp drop in strength. Further information is given in the publication available from Sirius Fire Safety Consultants ‘The behaviour of high strength bolts at elevated temperatures’.
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Q.
How do old structural steels behave compared with modern grades?
A.
Old structural steels are very similar to modern day mild steels. On a pro-rata basis they do not lose their strength at elevated temperatures quicker than Grade 275 for example. Since the design loads in use at the time when old mild steels were manufactured were somewhat lower by proportion, they would under the same fire conditions behave slightly better. Further information is given in the research publication ‘The application of BS5950: Part 8 on fire limit state design to the performance of old structural mild steel'.
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Q.
Is there a difference between composite and non-composite design?
A.
Yes, in composite design of floor systems the concrete is working with a steel beam in providing structural support. Shear connectors are welded to the top surface of the upper steel flange fixed either through metal decking or on either side of precast floor units over which concrete is then poured. In non-composite design the concrete slabs are providing just a floor and is just dead weight.
Some types of columns can also be designed for composite action in which a steel section may be encased in concrete with shear connectors, concrete columns cast containing reinforcing bars or infilling hollow sections with concrete and reinforcing bars or steel fibres.
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Q.
What are the different types of fire protection?
A.
There are over 60 fire protection products on the market. These can be categorised into 4 main types Boards e.g. plasterboard, vermiculite boards, calcium silicate boards, and mineral fibreboards.
Sprays e.g. vermiculite cement, mineral fibre, magnesium oxychloride Intumescent coatings, these are generally water or solvent based and are applied to provide thickness of between 0.2 to 5mm. There are several epoxy type resins that are used in particularly hostile environments and these may as much as 12mm thick.
There are also the traditional materials such as block, brick, concrete and even timber.
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Q.
Which fire protection systems are best for internal or external environments?
A.
Most board systems are unsuitable for external applications. Some intumescent coatings can be used externally such as the epoxy based systems as well as several of the thin film solvent-based systems. However, the latter would normally require a top sealant, which must be maintained to ensure long-term performance.
Several of the spray systems can be used externally and these are usually based around the vermiculate cements.
In addition concrete and brick may be used externally.
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Q.
Are test results in the UK the same as you might expect in the USA?
A.
Yes and no. Tests carried out in the USA use the standard E119, which notionally has the same rate of heating as that used in the UK and Europe. However the control mechanism for the furnace uses a thermocouple inserted in an iron tube. This slows down the response and as a result the furnace heats up at a faster rate than either a UK or European furnace. Failure temperatures may therefore be arrived at slightly earlier in a test. In addition, floor beams tested in the USA are restrained and this may result in an improved fire performance. In the case of floor beams these two factors tend to cancel each other out, but columns may not perform as well as in the UK.
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Q.
What is the effect of fire on other materials e.g. masonry, concrete, wood?
A.
Concrete and block work generally suffer irreversible loss in strength once these materials are heated to temperatures usually in excess of 300°C. At higher temperatures, up to around 600°C at least 60% of the strength is permanently lost. The compressive strength also continues to drop even during the cooling stages of a fire. In contrast however, hot rolled structural steel will regain virtually all of its strength when it cools back to ambient temperature from 600°C.
Wood chars at a certain rate depending upon the species and the fire source. In general uncharred timber retains its full strength, whereas it is usually assumed that charred timber has no strength at all. However, it should be noted that charred timber acts as an insulator to the unburnt material and the strength of a timber component can be assumed to be that of the remaining cross section.
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Fire Risk Assessment
Q.
How can you prepare for the changes in workplace fire legislation?
A.
The easiest way to prepare for the changes is to ensure that you are complying with the current fire precautions and health and safety regulations. The basic requirements of the current regulations are going to be carried forward into the new legislation. There will also be additional duties such as the safety of people not on the premises, and the safety of fire fighters will now have to be considered.
The average business professional operating within simple, small premises may be able to manage a satisfactory fire risk assessment. This will of course depend upon the competency of the person carrying out the assessment. Businesses operating in more complex, larger premises may need to call on the assistance of a fire safety specialist or consultant in order to undertake a satisfactory fire risk assessment. Examples of more complex premises will be commercial, residential, aviation, shipping, retail, and distribution and process premises.
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Q.
What does a fire risk assessment cover?
A.
Typically our assessment will include a review of the following (where applicable):
• Fire safety awareness and management,
• Induction training (fire safety) of employees, contractors and visitors
• Fire safety documentation, loss control programmes
• Housekeeping standards
• Means of escape
• Evacuation drill records
• Emergency lighting systems
• Compartmentation / building construction
• Fire protection systems
• Fire detection systems
• Fire alarm systems
• Smoke ventilation systems
• Fire protection / detection / emergency lighting maintenance records
• Electrical system maintenance including records
• Production plant maintenance records
• Control of hazardous processes and combustible / flammable materials
• Control of contractors
• Hot work procedures and controls
• Lightning protection
• Crane operator means of escape
• Spray booth operations and procedures
• Smoking controls
• Security / arson prevention procedures
• Pre-emergency planning / Major Incident Procedures
• Fire protection system impairment procedures
Fire fighting facilities / access for fire brigade intervention
Our fire risk assessment report can help you comply with your insurance requirements for your property.
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Q.
Why is a good fire risk assessment important?
A.
The results of a properly conducted assessment will be of benefit to the business, not only in terms of satisfying the legal requirements relating to safety of employees, but also in terms of providing a safer overall environment and reducing the risk of fire damaging or destroying the business.
There is no single way in which an assessment should be made or, at present, any National or International standards relating to fire risk assessment.
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Q.
So, what do you need to carry out a fire risk assessment?
A.
Knowledge
An understanding of fire safety
Many years experience in fire safety engineering/management
Documents to assist with the process i.e. Publicly available specification PAS 79 fire risk assessment
What is certain is that fire claims in commercial properties are on the increase and the claims figures for 2005 were estimated at over £800 million. This is not including the Buncefield oil depot fire. The warning is that although fires may be falling statistically according to the office of the Deputy Prime Minister the overall financial effect of those that do occur is becoming more serious. Companies must ensure that a robust and adequate fire safety management programme is introduced and maintained.
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Q.
Who is a 'Competent Person'?
A.
The Fire Safety Order calls upon ‘Competent Persons’ to carry out a fire risk assessment. The definition has not been accurately defined and may not be until there is a legal case in which the 'competent person' is expected to give evidence following a serious fire/incident.
As legislation is unclear on the competency of the fire risk assessor, the employer will need to decide whether they, or a member of staff, have the necessary experience and expertise to carry out a fire risk assessment in-house or whether external assistance will be required.
A competent person is someone who has thorough background knowledge and understanding of fire safety, together with many years experience in fire safety engineering and fire safety management, applying that knowledge.
We do not believe that sending a health & safety representative on a short course will equip them adequately to carry out a Fire Risk Assessment, suggest courses of action and if necessary be expected to defend their actions/decisions in a court of law.
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Q.
Why should you use an external, qualified fire risk assessor?
A.
Many businesses will look outside of the company to undertake a professional fire risk assessment, usually engaging external consultants. Some companies may feel that they have internal employees who are capable of undertaking this task.
A fire risk assessment requires honesty to positively highlight fire safety needs, weakness and recommendations. Sometimes the problem with internal staff carrying out the fire risk assessment is that they can be influenced by local issues such as:
• Budget restraints
• Fear of criticizing work processes
• Incorrect building layouts
• Shortfalls in senior managements fire safety procedures
• Time constraints and other work influences and pressures
There is also the question of competency. A fire risk assessment is not simply about ticking boxes, delivering a report and finishing there. We believe that to perform a thorough fire risk assessment, it is important to work with the existing Health & Safety personnel to deliver a complete service, based upon our expertise.
Sirius Fire Safety will support fire safety management across your company to help maintain the highest possible fire safety standards.
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