The purpose of this assignment is to critically assess the effects of the interaction between Life Safety and Property Protection, when considering the fire safety strategy for a large manufacturing and storage facility. Describe and justify the fixed fire protection techniques you would advocate using. In addition when considering the holistic approach discuss how this may affect the operational strategy of the fire fighting. (2500 Words)
Debate about warehouse fires has centred on the role of sprinkler systems and compartmentation, but a topic that is also important is smoke control. A smoke control system can provide occupants with a clear escape path, reduce the likelihood of damage to stock and allow firefighters to enter a building earlier and tackle a fire at source, increasing the chances of saving the building. The statistics for the 12 months from February 2008 to January 2009 show a decrease to only 10 fires, putting warehouses premises 5th in the league tables of worst offenders. Whilst warehouse fires had reduced the estimated losses were in excess of £13m, still 2nd behind factory losses.
Passive fire protection, which includes compartmentation of the relevant building through the use of fire-resistant walls (and floors where necessary). Compartmentation is an effective method of preventing fire spread, limiting fire damage to the room of origin, and providing a platform to enable occupants to reach a place of safety before conditions become untenable,
In order to formulate a rational approach to fire safety the first step is to identify the fire safety objectives that are to be met. Only then can the required fire protection measures be selected to achieve a safe, robust and economic design. There can be a variety of fire safety objectives for different buildings. The most commonly identified objectives are:
Within the UK life safety and prevention of fire spread are addressed by the Building Regulations. Asset protection and business continuity is not specifically addressed by the Building Regulations
Sprinklers systems are often encountered in modern day building design. They are provided to protect life and/or property against fire, and have been shown to do this effectively. A report published in 2005 by the NFPA based on the most recent data concluded: When sprinklers are present, the chances of dying in a fire are reduced by one-half to three quarters, and; the average property loss per fire is cut by one-half to two-thirds, compared to fires where sprinklers are not present.
A comparison of the reliability of sprinklers compared to passive fire protection can be found in PD 7974 - Part 7 Application of fire engineering principles to the design of buildings.
In most situations sprinklers are considered as an option, with an associated trade-off. The word 'trade-off' is used to describe a concession that is made in recognition of the benefits that sprinklers provide in relation to life safety
Fire safety measures
For Fire Safety of the building, the functional requirements are set out in Part B of schedule 1 of the Building Regulation 2000 and are divided into 5 areas these are:
• B1 Means of Warning and Escape,
• B2 Internal Fire Spread (lining),
• B3 Internal Fire Spread (Structure),
• B4 External Fire Spread and
• B5 Access and Facilities for the Fire Service.
To comply with the functional requirements the Secretary of State has approved a series of Approved Documents, which aims to provide practical guidance with respect to the functional requirements of schedule 1 and Regulation 7 of the Building Regulations 2000(SI 2000/2531) for England and Wales. The Approved Document for the above function is Approved Document B (Fire Safety), Volume 2-Buildings other than Dwelling houses (ADB); however these functional requirements can be achieved in a number of alternative ways.
It is not possible to meet the functional requirements of the Building Regulations for a very large single storey warehouse building purely by reference to prescriptive documents. The principle areas of non-compliance with respect to life safety are:
Excessive travel distances,
Ambient sound levels in warehouse, due to constant operation of machinery,
Break Glass Call Point coverage, due to layout of racks and picking stations,
Provision of a life-safety sprinkler system
Areas of non-compliance with regards to property protection are:
Fire Service hydrant coverage,
Compartmentation,
Provision of smoke ventilation
Approved Document B (ADB) gives recommendations on the requirements in relation to Fire Safety measures for industrial and storage buildings in England & Wales (Scottish and Northern Ireland building regulations apply elsewhere). Where these recommendations cannot be met, trade-offs are allowed and a key one is the limitation on travel distances. In such buildings there is a limit to the travel distance of 25m where travel is possible in one direction, and of 45m where travel is possible in more than one direction.
Figure
Figure
Where travel distances are to be extended, a smoke control system designed to BS 7346-4 may be accepted to compensate as part of an engineered scheme. British Standard BS 7974 Fire safety engineering in buildings and supporting published documents (PDs) provide a framework and guidance on the design and assessment of fire safety measures in buildings. Following the discipline of BS 7974 should enable designers and Building Control Bodies to be aware of the relevant issues, the need to consider the complete fire-safety system and to follow a disciplinedanalytical framework. This automatically directs the designer to the BS 7974 suite of documents, and it can be seen by reference to BS 7974 Part 6, that compliance with the guidance relies on "Management Level 1", which is very similar to the requirements of BS 9999
Figure
Figure
ADB also specifies that the maximum floor area of an unsprinklered single storey building should be no greater than 20,000 m2. A smoke control system may be installed as a compensatory measure as part of an engineered scheme to increase the floor area. Where local Acts are in force, these require additional fire protection measures to ADB for industrial and storage buildings. Typically, where such buildings exceed 7,000m2 then either a sprinkler or a smoke control system is required for firefighting access. Where such buildings exceed 14,000m2 then both a sprinkler and a smoke control system is required..
The Fire Safety Order reformed the law relating to fire safety in non-domestic premises. Specifically it replaced the Fire Precautions (Workplace) Regulations 1997 and the Fire Precautions Act 1971. It imposes a general duty to take such fire precautions as may be reasonably required to ensure that premises are safe for the occupants and those in the immediate vicinity. By virtue of the Order, the responsible person is required to carry out a fire risk assessment of their premises. This must be a suitable and sufficient assessment of the risks to which relevant persons are exposed for the purpose of identifying the general fire precautions they need to take to comply with the requirements under the Order.
Although these requirements are applicable to premises whilst in operation, it is useful for the designers of a building to carry out a preliminary fire risk assessment as part of the design process. If a preliminary risk assessment is produced, it can be used as part of the Building Regulations submission and can assist the fire safety enforcing authority in providing advice at an early stage as to what, if any, additional provisions may be necessary when the building is first occupied.
Life Safety and Property Protection
ADB 2007 allows the non-compliance to be addressed through the use of specific fire engineering design. Thus there is no obligation to adopt any particular solution contained in an approved document if you prefer to meet the relevant requirement in some other way."
Figure
Proposals may be reviewed and assessed against the functional requirements of the Building Regulations and the recommendations contained in the associated technical guidance documents applicable to this type of Premises and the use to which the building will be put once occupied. Recommendations contained within a strategy are intended to address the principal aim of the Building Regulations, this being to secure a reasonable standard of health and safety to people in and around a building. However, provisions should, or may also serve to provide a significant high level of protection to the fabric and contents of a building in the event of a fire.
A performance based approach to means of escape design can take the form of a time based comparison between: The time required to reach a place of relative safety (Required Safe Escape Time - RSET). The time available for occupants to reach a place of relative safety prior to untenable conditions being achieved (referred to as the Available Safe Escape Time - ASET), and; the aim of a performance based design is for RSET to be less than ASET, to allow safe evacuation. A detailed explanation of the approach can be found in PD 7974-6:2004. However, the key features of the approach and the impact of sprinklers can be summarised as follows: RSET is the sum of the fire detection/alarm time, the recognition/response time and the travel time to a place of safety. Sprinklers can help to reduce RSET by detecting a fire at an early stage. ASET is determined by the onset of untenable conditions within the area being considered untenable conditions can be caused by smoke toxicity and heat from fire and/or smoke. Sprinklers can help to extend ASET by limiting the amount of smoke production from a fire and by reduction heat exposure. Trade-offs relating to travel distance is more likely to be realised if fast response sprinkler heads are provided. In a similar way, sprinklers could be used to justify a shortfall in the exit width provision in a building.The most comprehensive method for calculating escape and evacuation times involves the use of computational models in which the physical characteristics of building spaces and escape routes are represented.
It would be necessary to model numerous "worst case" scenarios, which in the case of a warehouse will be an ultra-fast fire on the ground floor, as it will typically create the greatest heat output and produce the largest quantity of smoke. Once the worst case scenarios have been determined, it's then necessary to factor in a degree of safety to take into account the fact that the design is only computer based.
By varying the parameters, a profile of evacuation times can be estimated for a range of scenarios. The diagram is taken from BS 7974:2001 , and reprised in AD "B". It shows part of a timeline comparison between fire development and evacuation/damage to property, and is commonly used in Fire Engineering, although the diagram below shows a timeline for critical damage to property/business. This type of diagram is used to summarise the fact that a set of deterministic criteria have been met - in this case, evacuation is completed before the tenability limit is reached, with consideration given to a safety factor.
Figure
Whilst there's no requirement to sub-divide a single storey sprinklered warehouse Insurance requirements dictate that some form of separation is usually necessary, depending on the size of the warehouse.
The contents are usually 'high fire risk' as defined in the Approved Document (Table 3, Note 6) which normally limits the travel distances to final exits to 25m.
Figure
BS5839 gives direction as to the spacing requirements for Break Glass Call Points and Sound Levels. Guidance indicates that no one should have to travel more than 45m to a Call Point, and that ambient noise levels shouldn't exceed 90dB.
Effect relating to operational strategy of the fire fighting
In the Secretary of State's view the Requirements of B5 will be met:
A. if there is sufficient means of external access to enable fire appliances to be brought near to the building for effective use;
B. if there is sufficient means of access into and within, the building for firefighting personnel to effect search and rescue and fight fire;
C. if the building is provided with sufficient internal fire mains and other facilities to assist firefighters in their tasks; and
D. if the building is provided with adequate means for venting heat and smoke from a fire in a basement.
These access arrangements and facilities are only required in the interests of the health and safety of people in and around the building. The extent to which they are required will depend on the use and size of the building in so far as it affects the health and safety of those people.
Figure
9999 does not provide distances but says hydrants should be provided near to entrances including entry points to fire fighting shafts and that it is necessary consult with water authority, fire service and building control on requirements. Also 9999 references BS9990 which ADB does not. and recommends full consultation with fire service on what is required
Single-storey buildings can have a ground floor area of massive proportions, sometimes in the region of 20,000 or thereabouts. They may have numerous galleries and high bay racking. While fire can gain access to these high bays very quickly, it is a different matter from the firefighting perspective. BRE research shows that fire may reach the top of 10 metre high racking within as little as two minutes. A typical fire brigade response would allow three to four minutes for alarms, nine minutes till first arrival, to set up, typically 20 minutes to be effectively operational.
The complexity and potential dangers of firefighting in warehouse and distribution buildings require careful and extensive pre-planning by fire brigades, warehouse operators and other agencies
Fire safety legislation and Building Regulations are limited to minimum provisions for life safety. They have not necessarily kept up with developments in modern construction or the materials that can threaten the life safety of rescue services. Fire brigades will champion the installation of sprinklers in warehouse buildings but there is no statutory requirement for them.
It is not always possible to achieve the full requirements for firefighting access recommended by the code due to site constraints. This could potentially impact on set-up time for firefighting operations and/or reduced ability to fight a fire and save lives. In such situations the fire authority may consider the use of a sprinkler system a compensatory feature as the fire is likely to be controlled to a smaller size than if unsprinklered. This takes into account fire service arrival times and potential fire sizes on arrival.
Summary
The principle concern of a building of this type is the ability of the occupants to make a safe escape in the event of fire and the ability of the FRS to undertake any search and rescue operations and firefighting activities. It's also really important to ensure that any agreed strategy is maintained throughout the life of the building, and that any changes are suitably addressed before they are implemented, in order that safety can still be guaranteed. Article 29 of the Regulatory Reform (Fire Safety) Order 2005 gives Fire Authorities the power to serve an Alterations Notice if the Authority is of the opinion that the features of the premises, their use, any hazard present, or any other circumstances, may constitute such a risk (to relevant persons) if a change is made to them or the use to which they are put.
Figure
It would be unfitting to comment on the tragic consequences of the 2007 fire at Atherstone. However it is generally accepted that sprinklers in fully-protected buildings provide such a high reliability of probability of successful containment or extinguishment of a fire that it is most unlikely that fire-fighters responding to a fire in such a building would be exposed to significant risk from the fire or its products.
