The Diamond synchroton, the largest scientific built in the UK for almost 30 years, presented some very special challenges. The solutions devised by Safe Consulting won them the runner-up position in the FSE Design award, sponsored by BT redcare.
The Diamond synchrotron light source is the largest scientific facility built in the UK for nearly 30 years. This giant machine, called a synchrotron, could be described as a series of ‘super microscopes’, housed in a futuristic doughnut-shaped building nearly three quarters of a kilometre in circumference, covering the area of five football pitches. It will produce incredibly intense light beams, mainly as X-rays, that can penetrate deep inside all kinds of matter, to support pioneering research in the life, physical and environmental sciences.
The functional requirements of the synchrotron building as a quality experimental facility were the driving forces behind the design. As such, all fire safety recommendations attempt to fall in line with the building’s functional design, while not sacrificing the key issue of the life safety of occupants.
Means of escape
The main life safety issue in any building is to ensure that in the event of a fire, people are able to escape to a place of relative safety in a controlled manner. Due to the unique fire risks present in buildings such as synchrotrons, additional and specific prescriptive fire safety advice is provided under the Fire Certificates (Special Premises) Regulations 1976. But in this case, the size and complexity of the Diamond Synchrotron does not allow the recommendations in the Regulations to be achieved in full.
A bespoke evacuation methodology was developed to enable people directly affected by fire or smoke, to safely escape to the exterior of the building. Meanwhile, those further away from the fire will be warned of an incident, so enabling them, if needed, to terminate experiments in a controlled manner.
As a consequence of Safe Consulting’s strategy, people in the building are constantly made aware of their location. This is achieved with signs displayed in prominent locations in each sector and a colour colour-coded scheme, while the building’s fire alarm warning system (in this case a pre-recorded voice alarm message) is designed to distinguish between these areas. To achieve this, the main experiment hall was essentially sub-divided into 12 equally sized radial alarm/evacuation and smoke zones, as shown in Diagram 1. Each is a 300 segment and each contains one of the 12 perimeter escape cores that serve the perimeter plant room, office and laboratory levels (each zone was subdivided into two sectors so there are 24 sectors in total). The remainder of the building, predominately plant areas, was sub-divided into 13 separate service area zones.
A number of the prescriptive travel distance recommendations are exceeded in the building. This is purely as a consequence of travel distance being a function of building geometry, which is defined by the machine itself. SAFE was able to demonstrate that although the travel distances in some areas may appear excessive, the time it takes a person to reach a place of relative safety (bearing in mind the place need not be outside the building) is not unreasonable, as it is not the distance an evacuee has to travel that is important but the time taken to do so.
Three methods of escape for the building were initially considered:
– Tunnel escape. A number of foot tunnels beneath the building were considered. This was rendered impossible, however, because of the need for extremely stable foundations to minimise differential movement and vibrations.
– External bridges. The use of external bridges over the roof of the synchrotron from the central courtyard were considered but this proved impractical due to the presence of a moveable crane.
– Internal bridges/stairs/ladders. It was concluded that the most effective escape solution – both in terms of the efficient movement of occupants and its ability to satisfactorily integrate into the functional design of the facility – was to provide six internal crossing points to enable occupants to travel over and across the storage ring. This is shown in Diagram 2.
To demonstrate that these extended distances do not present a significant risk, a means of escape analysis was prepared for a number of discrete areas within the building, referred to below as ‘risk areas’.
To determine what is an appropriate ‘escape period’ for these various risk areas, the evacuation of occupants was broken up into its constituent elements. Each step was subsequently assigned a duration, depending on building parameters and the capabilities of evacuees. This then enabled an approximate total evacuation time to be calculated for the area of the building under consideration.
By using CIBSE Guide E calculations and STEPS (Simulation of Transient Evacuation and Pedestrian movementS) evacuation modelling software, Safe Consulting was able to prove that the escape times – under the worst case fire scenario – were within acceptable time periods, especially as the smoke control system was designed specifically to accommodate the extended escape travel distances.
The experiment hall area of the synchrotron building has an approximate gross internal floor area of 21,000 square metres. The prescriptive compartmentation recommendations, therefore, contained in Approved Document B (which for an unsprinklered industrial building is a maximum floor area of 7,000 square metres) could not be satisfactorily achieved, which would have resulted in the building having to be sprinkler protected.
But as the purpose of compartmentation is to reduce the risk of a fire becoming large, this was overcome by an alternative to large full height sub-dividing walls, as recommended within the prescriptive guidance. A scheme of ‘micro-compartmentation’ was implemented so that all areas of potential fire risk were housed within fire resistant enclosures to prevent rapid fire spread.
Instead of following the prescriptive recommendations which would have required three equally sized compartments of 7,000 square metres, the following micro-compartments were formed:
– Each hutch, through which the synchrotron light beams are transported and where the research experiments are carried out, is separated from one another by 30 minute fire resisting construction.
– The storage ring enclosure occupies approximately 4,500 square metres of the experiment hall and was considered to be one compartment. Although not fully fire sealed, the number of openings did not present a risk to the spread of fire, so maintaining the fire compartment principle.
Although the remaining compartment exceeded the ADB maximum size by some 2,300 square metres, this was not thought to provide any less safety due to the presence of the hutch compartmentation. As the hutch compartmentation comprised 48 individual sections, this provided a vastly increased level of separation. As such, the level of compartmentation was considered adequate and sprinkler protection was therefore not deemed necessary, also bearing in mind the height of the roof over the experimental hall.
Smoke control
The experiment hall is to be fitted with a smoke control system, to ensure that routes of escape would be sufficiently free from smoke during the phased stages of an evacuation. In order to achieve this, the experiment hall is sub-divided into ‘smoke zones’ (each approximately 1,600 square metres) separated from one another by drop down smoke curtains, with each zone containing three fire-rated extract fans. The curtains are designed radially around the experiment hall, forming smoke reservoirs that sub-divide the building into 30 degree segments. The positioning of the curtains was such that each smoke zone contained a single stair core.
On a double knock signal from the smoke detection system, all 12 smoke curtains automatically activate and lower to a calculated point. This achieves the design objectives in the experiment hall, yet still allows a sufficient clear space to enable adequate movement for the occupants.
The system had to ensure that any smoke in the building would not ‘build down’ to a point less than 2.5m above the floor level of the first floor office balcony for at least 30 minutes. In order to assess the level of smoke extraction required to for a sufficient period to enable people to escape within the fire affected zones, smoke production calculations were carried out.
The ground and first floor perimeter laboratories and offices are internally subdivided into fire resisting construction compartments of 32 square metres each. So it was assumed that a fire in the laboratories or offices would be prevented from breaking into the experiment hall for a sufficient period of time to allow evacuation. As such these locations were not considered as a fire model in the smoke generation calculations.
A variety of potential hutch designs may be provided in the building and so smoke control solutions were developed for all possible configurations. The following common features were provided for each hutch design:
– The control hutch (which predominately contains personnel and PCs/electronic control equipment) is a sealed box formed of 30 minute fire-resisting construction. The entry door is 30 minute fire rated and has a self closing device – therefore a fire within the control hutch was not included as a potential fire model.
– The construction separating the hutch sections is 30 minute fire resistant.
– The remainder of the hutch construction, being lead lined, will achieve 30 minutes fire resistance.
Due to the weight of the lead lined doors, automatic closure was considered problematic. This was taken into account with the smoke control design.
Exhaust gases from the experiment hall will consist predominately of air mixed with smoke during its movement from the fire source to the extract ventilators. Fresh air is needed to replace it at a rate equivalent to the smoke exhaust rate, and at a height low enough not to prematurely mix with the smoke being extracted.
Push-pull systems (ie. mechanical extract and replacement) are not generally recommended, due to the possibility of differential pressure gradients in the experiment hall, which would adversely affect the efficiency of the smoke extract system. As such, inlet air for the building’s extract system is provided naturally, via the automatic opening of the smoke extract fans in all smoke control zones other than those in extract mode. This can be achieved, as the underside of each extract fan is provided with an automatically opening insulated shutter, so connecting the experiment hall space directly with fresh air. For a single zone in extract mode (three fans in operation) 33 fan units would be in the ‘open’ position passively providing make up air.
From the calculations produced, it was concluded that potential hutch tenants should provide one of two fire safety measures in order for its smoke generation potential to be within the limits of the building’s smoke control design:
(i) Forming the entire hutch from 30 minute fire rated construction (excluding doors, except that of the control hutch), or
(ii) Providing the entire hutch with some form of local fire suppression.
Both these solutions enable the objectives of the smoke control system to be achieved and therefore the ‘mixing and matching’ of these solutions between adjacent hutches was considered acceptable.
This fire engineered solution took what is a very unusual building and applied the principles of prescriptive fire regulations to produce a tailor made solution. The solution took a series of calculated trade offs, concentrating on means of escape, compartmentation and smoke control.
Picture 1: Model of the synchroton showing individual ‘hutches’ to be leased to different tenants.
Picture 2: Aerial photo of synchroton under construction.
Figure 1: Ground floor plan showing radial alarm/evacuation and smoke zones.
Figure 2: Section through synchroton building showing means of escape solution.
