Maintain your integrity
Published: 01 October, 2008
The term “passive fire protection” is used to describe a number of materials and systems of construction intended to delay the passage of fire from one part of a building to another. It is also true to say that it tends to be a “fit and forget” issue – largely because the occupiers and users of the building don’t fully appreciate its importance to the overall fire protection of the structure, its contents and its occupants.
While a new build may comply with the relevant regulations and have all its passive protection installed correctly, the problems begin as the building ages. Business tends to be dynamic and this means that the premises a company occupies must adapt or be adapted to meet the changing needs of the occupier. Unless these changes are carefully thought through, simply installing a new cable run to supply a new appliance may compromise several barriers which form part of the fire protection for means of escape or adjoining compartments. If this is not addressed it may become a case of progressive degeneration of the passive fire protection which will eventually lead to a complete failure.
By definition, passive fire protection means those elements, some of which may be structural, which are intended to prevent the passage of fire from one part of a building to another for a specified time. This includes devices or sealants intended to prevent the passage of heat or smoke through ducts or other openings, curtains in roof voids and atria, and materials fitted to cable runs or trays to restrict flame and heat transmission. In industrial premises it will include shutters in walls penetrated by conveyors or roller paths, seals on pipes, cables and other services run through walls or floors and safety systems installed to prevent heat transfer from one area to another.
Many building Codes require a minimum of 30 minutes’ fire resistance in partitions or walls, but, in the marine industry and the offshore industry, fire resisting structures may be required to resist the passage of heat and flame for up to 240 minutes – though that is an extreme example. The majority of bulkhead and deck systems used in these applications are either 60-minute or 120-minute systems.
What owners, managers and engineers need to keep in mind is that this is a minimum requirement and is usually the minimum performance required for the weakest element in the wall or floor which may be a door, a duct or a pipe or cable run.
Passive fire protection plays a vital role in the safety of the occupants, yet it can only do this if its integrity is maintained and it has been properly fitted in the first place.
The most obvious example of a “passive” element is the humble “fire door” intended in the UK to hold back the passage of fire for a minimum of 30 minutes. It can do this only if the door is fitted into a frame intended for that type of door – in other words a frame designed and tested to the same standard and built for that door. Next it must have the specified door furniture and be hung in accordance with the original specification and test certificates. While this may seem obvious to the designers, engineers and fire safety specialists who are involved in the planning and construction, the problems begin as soon as the building is handed over.
By their nature doors are subjected to a considerable amount of normal wear and tear in day to day use. The strain on the hinges imposed by the weight of the door and the door closure mechanism can cause the door, eventually, to sag. Once this happens the door may not close fully, leaving a gap through which heat and smoke may be transmitted in a fire. Worse is to have a door subjected to heavy traffic where the “hold-open” device is placed at the opposite end of the door to the closer. This causes the door and the frame to be subjected to quite severe stresses in opposition to one another and eventually the door may close when released, but it will have warped and will not close effectively or completely. This does not mean that such devices should not be used, rather that they should be given proper consideration and not left to the fitter to decide the easiest and quickest method for their convenience. As a recent major loss fire in the Midlands (UK) demonstrated, properly fitted fire doors can and did prevent a fire which destroyed the entire warehouse area from spreading into the office block with access into the warehouse. The same can be said of the fire resisting wall that separated the two areas. The wall had no weak points and no openings and held throughout the six hour fire, admittedly helped at the final stages by the fact that the fire and rescue service were by then using it effectively and ensuring that it did not fail.
Dry walls should be constructed in such a manner that the joints between boards are not “back to back”. This may seem obvious, but it is not always practised and once the joint has been sealed with mastic, and papered over, it may appear sound – but there is a danger that the failure of that hidden joint can compromise the entire dry wall if the fire then penetrates the second joint.
Nor should we overlook the effect of the openings made in such partitions to let in the boxes for the electrical fittings such as switches and sockets. Once again the opening creates the opportunity for fire to pass into the cavity, once again threatening the integrity of the wall unless it has been constructed properly in accordance with the system tested by the manufacturer.
Compartment walls are vital to the fire defences of any structure and not only because they protect parts of the operation or the occupants’ escape route. It is important to remember that, if the fire and rescue service is to be effective, they will need to be able to rely on these barriers to protect their teams entering the building to fight the fire. Effective fire fighting cannot take place from outside the building, but, to enter it, the fire fighters need to be able to do so safely.
Air vents in bulkheads are obvious openings, but how often do the users look at the concealed spaces above their heads? I would suggest that there is frequently no control of these spaces, yet, again, most building regulations make requirements for smoke and fire barriers in voids. Not infrequently these are compromised quite early in the building’s occupation, usually through lack of appreciation of their role, when some change of light fittings or the installation of new ducts or cables requires their being moved, deformed or penetrated.
This brings me to the second important point regarding passive fire protection. It is essential that everyone in a building understands the need to ensure that walls, doors, service ducts, sprayed on materials coating steel columns, beams and pillars all have a vital role in ensuring that fire spread is limited, retarded or controlled while the occupants escape – and the firefighters enter to attack the fire.
So, the question now is; what has this to do with the building user and their management of their activities within it? The simple answer is – a great deal. The Regulatory Reform (Fire Safety) Order in England and Wales, the Fire (Scotland) Act in Scotland and similar legislation internationally as well as a raft of regulations affecting the maritime and offshore industries all require the assessment of risk for occupier safety and place the responsibility for this on the “responsible person”. Nor does it end with the “risk assessment” for as all those who have this responsibility know, these are dynamic and the risk changes whenever something in the matrix changes and that can be as simple as the electrician compromising the integrity of a fire resisting wall or barrier. This may be particularly important in any very large uncompartmented structure such as a warehouse or factory where the use of portal frame construction may depend on the steel being adequately protected from the effects of fire. These buildings may well be provided with “active” fire protection systems in addition to their passive elements, yet the two are dependent upon each other in the overall protection of lives and the assets.
The key to the success or failure of a building’s passive fire protection in a fire lies with its maintenance. If the walls, partitions, doors, cable and duct penetrations and their related protection measures are rigorously defended and maintained, they will do the job they were installed to do. Unfortunately, in far too many cases, they are not maintained and the result is fire spread and fire damage which could and should have been avoided.
A relatively simple change can compromise an adequate fire barrier, as with a hotel which had brick-enclosed staircases. The enclosures were sound, until a rerouting of pipes needed for a heating system required the penetration of the enclosure on every floor, and the openings were not then resealed. As these were also hidden behind a board lining, no one spotted the danger until a fire in the basement resulted in smoke filling the staircases and rendering them unusable.
In industry, the extensive use of insulated panels to separate hot areas from cold can result, as a fire in a food preparation plant in Herefordshire recently demonstrated, in a very rapid fire spread. Expanded Polyurethane insulated panels offer light weight construction, ease of installation and considerable strength, but they do not have a great deal of fire resistance. Any joints need to be maintained and “stopped” with materials that will not allow easy penetration by flame. And some applications should not be considered at all, such as the use of profiled Polyurethane slabs to form internal walls and external curtain walls in multi-storey buildings. Unbelievably, this was seen recently in the Middle East on a construction site for a building over eight storeys in height.
Building managers and maintenance engineers need to be alert to any possible risk that may arise which could compromise their building’s structural passive protection. Buildings are dynamic, the risks within them change all the time. There can be no reason to increase the risk unnecessarily by allowing a contractor to compromise your passive fire protection and jeopardise your workers and your assets.
