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Last edited 04 Dec 2020
Joined-up thinking is key to building safely
Touching upon 18 different interfaces and providing vital utilities such as water, ductwork and electrics, a riser shaft is like an artery – an intrinsic part of any tall building. Although it serves an essential function, riser zone design is not taken as seriously as it should; meaning designers, contractors and the like expose themselves and others to risk, which can be avoided if the riser zone is given the attention it needs from the earliest point of design.
With the HSE’s new building safety regulator able to oversee the safe design, construction and occupation of high-risk buildings, mitigating risk has never been so vital. Riser zone design is a key ingredient to eliminate risk in a building, yet why is its significance so frequently bypassed? More importantly, which implications does this have on the overall safety of a building?
Look at any multi-storey building across the world and a riser shaft will be inside. Although a core component of every high-rise, riser zones are rarely designed efficiently. This is borne from differing beliefs in perceived responsibilities, the split approaches to writing specifications and the disconnection between construction packages. The lack of focus on riser zone design is further compounded by the fact there isn’t a category for riser zones within the system, Uniclass; astonishing when considering this is the industry’s go-to classification used across design and construction.
Moreover, according to General principles of prevention outlined in CDM 2015: Managing health and safety in construction, duty holders, including designers, are instructed to avoid risk where possible when designing a building. Although a riser is part of a designer's principles of prevention, it is not being included in the blueprint, which means there are loopholes in this guidance. It leads to the conclusion that designers are failing to meet their legislative obligations by creating a governless hole within a building, which is a huge hazard when working at height.
Designers might consider the walls, doors and floors around a riser, but in doing so they effectively create a shaft, which during construction also acts like a chimney in the event of fire. It is a risk highlighted in HSG 168 – Fire safety in construction, and the Joint Codes of Practice – Fire prevention on construction sites, but rarely mitigated by the designers in their design risk assessment, as required in CDM 2015.
Failing to consider this problem from the outset is a recipe for chaos. When constructed properly, the design of the riser walls and doors will contain the spread of fire. However, by not specifying the type of flooring used at every level within a riser they may be significantly adding to the risk if the walls/doors have not been installed correctly. Or, as is more likely, they are modified as new commercial or domestic tenants come and go, amending the M&E services that enter their domain from the riser without adequately replacing the fire seal. Furthermore, other functions that interface the riser zone can cause difficulties in closing off paths for fire. Although designers might believe they have contained risk, they are actually adding to it.
It goes without saying that riser-related issues should be addressed at the design stage so that fire can be contained if and when it occurs. Joined-up thinking therefore is essential, particularly when applied to construction. It displays a visionary-like ability to implement complex and fragmented plans, resulting in buildings that remain safe and long-standing. This is best achieved by designers taking a holistic approach to a structure’s design, and that means factoring in details such as the riser flooring, which too often falls through the gap in their professional thinking.
 What are the options?
Glass reinforced plastic (GRP) grating is generally seen as a safety solution to prevent people falling through holes, but how effective is it? There are three basic resins that are used to bind the glass fibre strands to form GRP: orthophthalic (ortho) resin; isophthalic (iso) resin, and phenolic resin.
Ortho resin GRP is the cheapest entry-level GRP which readily burns. Iso resin GRP grating is said to meet BS 476-7, the regulation relating to the measure of the surface spread of flame, but only in flat sheet form, tested vertically (so grating cannot meet that test). However, when installed in a riser’s chimney-style environment, Iso GRP grating is found to be extremely flammable, a dormant fuel cell. This makes the BS 476-7 classification unsuitable for its use within a riser zone.
Neither Ortho nor Iso GRP grating is used on offshore oil platforms or the London Underground for fire and smoke reasons, yet it is readily used in high-rise construction. Surely, if we are paying more than lip service to the risk of fire shafts, then either Phenolic GRP (identifiable, as it is red/brown in colour) or steel maintenance platforms should be used.
If a main contractor decides to use GRP grating as the maintenance flooring and installs it, it adds to a building’s smoke and fire loading in both its under construction and final state. It is absolutely crucial, therefore, that the appropriate materials are specified to prevent falls and maximise occupant safety in the event of a blaze. You may question why the main contractor has decided on the maintenance flooring. The answer is simple: because no one in the design team has considered anything else.
There are other issues with GRP, some of which relate to a lack of understanding of its properties. Installers will often over-cut it when installing mechanical, electrical or plumbing services within a riser shaft. This weakens the GRP, causing it to lose its integrity. To compensate, steel beams are often used to bolster the area beneath the GRP; a lengthy and potentially perilous process involving working from height off scaffolding, and some form of fall arrest such as a handrail.
One Crown Place is a mixed-used development which features two residential towers located over a six-storey office podium. On the One Crown Place project, the Mace Construction/Mace MEP teams required a system that would help manage the many risks and challenges faced with the buildings’ risers.
One of the challenges faced during the construction of the project was the risk of falls from heights in riser shafts that required fire walls passing through them and horizontal fire protection. To eliminate this risk, the team specified RiserSafe® from Ambar Kelly, a full riser management system which combats many construction-related issues including eliminating the risk of falling from height. Mace worked with Ambar Kelly, who provided a total of 729 of its RiserSafe® units, which accommodated all interfaces associated with the concrete frame, steel frame, M&E services, dry wall and blockwork. The bespoke units were simply cast into the structural floor slab, forming and protecting the hole in one action. This approach eliminates risks associated with working at height and the spread of smoke and flame.
This type of riser solution removed the need for riser shaft management tools such as permits, daily inspections of scaffolding and temporary fire doors. The offsite co-ordination reduced onsite subcontractors’ time and cost and contributed to removing the intense day-to-day management on site to ensure operatives were working in a safe environment and projects could be delivered efficiently. The cost-effective system saved the project over £300k due to eliminating alternative work, materials and processes required to protect the riser shafts during construction.
HSE standards indicate that buildings over 18m must have sufficient horizontal compartmentation every 10 floors to prevent the movement of smoke and flame rising through the shaft, up and down the building. A product such as the likes of RiserSafe®, which has been fire tested by the BRE, has a steel floor plate on top which acts as a horizontal fire barrier to the spread of smoke and flame on every level that it is used. If there is a 50-storey building with a unit cast in at each horizontal floor, fire cannot spread as there is a solid steel durbar plate sitting on top, blocking its path.
The construction industry needs to incorporate fire resistance into fall protection decisions, looking at each project holistically to account for all the variables. By designing the riser zone, multiple benefits can be reaped and many risks can be eliminated. If efficient measures are employed to fill in the riser void, then frankly there is no risk of workers falling from height.
Although this might seem like a simple message, it still needs to be reiterated and circulated around the industry. If the riser zone is a core part of a safe, efficient building then how long will it be before it becomes a core factor in building design? With some joined-up thinking and a holistic approach taken by architects, the question of ‘Who’s responsible for the riser?’ will go some way to be being answered.
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