Working on Cold Store Ceilings

2022-09-30 Source: www.refindustry.com Collect Reading Volume: 3267
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The Institute of Refrigeration technical committee has published the new technical guidance note on working on cold store ceilings. The guidance relates specifically to insulated cold and chill stores that are constructed within a building structure with ceiling panels that are supported by that structure, typically using drop rods suspended from a portal frame or building truss.   

Many refrigerated warehouses and factories are constructed from composite insulated panels which provide a barrier to heat and moisture gain from the surroundings. Accidents and near misses over many years have shown that the original design may be insufficient to safely carry in-service or maintenance loads and can be seriously compromised by degradation of the insulation material or the support structure.  
The purpose of this Guidance Note is to provide a reference for good practice in design of these buildings and their use and maintenance. 

The source:  ior.org.uk

Find also links  to useful further information such as the IOR Cold Store Code of Practice, HSE alerts and key legislation and standards in the end of the guidance.






Introduction

This guidance note relates specifically to insulated cold and chill stores that are constructed within a building structure with ceiling panels that are supported by that structure, typically using drop rods suspended from a portal frame or building truss. Smaller cold stores may be self-supporting and the guidance in this note should be applied to them as appropriate, with particular attention paid to the load-bearing capability of the structure and the need for edge protection.
Many refrigerated warehouses and factories are constructed from composite insulated panels which provide a barrier to heat and moisture gain from the surroundings. Guidance on the design of cold store ceilings is given in the Institute’s Cold Store Code of Practice (2015) but this doesn’t give design figures for the load carrying capability of the ceiling. Accidents and near misses over many years have shown that the original design may be insufficient to safely carry in-service or maintenance loads and can be seriously compromised by degradation of the insulation material or the support structure. The purpose of this Guidance Note is to provide a reference for good practice in design of these buildings and their use and maintenance.
The Health and Safety Executive published a Safety Alert “Deterioration and failure of cold/frozen food store ceilings” in November 2010 (reference CON 4-2010) and refreshed it in October 2020. It was distributed as a Technical Bulletin by the Institute’s RACHP Engineering Technicians Section (reference TB-21 dated October 2020) to raise awareness of this issue, in particular the consequences of degradation of older installations. Other guidance is also available and some links are given at the end of this document.
Approved Document B (Fire Safety) of the Building Regulations (2019) recommends that insulation envelopes (particularly ceilings) should be designed to prevent early collapse. As such, it is recommended that ceiling panels should not only be supported by insulated walls but should be independently supported otherwise a sudden and catastrophic collapse of the ceiling could occur if one of the walls is damaged, for example in a fire or by vehicle impact.

Design basis

Where an insulated cold room is constructed within a building structure the design should minimise the extent to which services are located within the space above the insulated room, known as the roof void. Where the positioning of services in the roof void cannot be avoided then permanent walkways with suitable stair access and egress should be incorporated into the design to eliminate the need to walk on the insulated panels. Many cold store ceilings are designed to support the minimum requirement in BS EN1991-1-1:2002 (which superseded the British Standard BS 6399-1:1996 but retained the same requirements).

The ceiling’s capability is given as a uniformly distributed load (qk) and a single concentrated load (Qk), assumed to be imposed on an area not exceeding 50mm x 50mm square in the mid-span. These are given in kN m-2 and kN respectively. Note that for general assessment of loading 1kN is approximately equal to 100 kg. The minimum requirement for ceilings that are not intended to be used as a working platform is qk = 0.25 kN m-2 and Qk = 0.9 kN. This requirement can be found in clause 6.4.3.2(8) of BS EN 1991-1-1 and is also in clause 5.2 of BS 6399-1. This is the loading often described as “one man and his toolbox” but this imprecise description is problematic and should be avoided. It doesn’t acknowledge that both workers and toolboxes come in all shapes and sizes. It also doesn’t recognise the ways in which load bearing capacity can decrease over time.

Structural platforms may be installed permanently in a building or could be a temporary structure, for example scaffolding, while work is completed. The load bearing capacity of permanent structures depends upon the building purpose, but even the requirements for floor load bearing capability in a domestic setting given in BS EN 1991-1-1 are substantially higher than those for a cold store ceiling, with qk = 1.5 kN m-2 and Qk = 1.4 kN.

Where temporary scaffolding is constructed, the loadbearing capacity is also dependent on the purpose of the scaffolding. This is detailed in the National Access and Scaffolding Confederation’s design guide, TG20. The requirements of TG20 together with requirements for domestic settings, offices and general storage are set alongside the typical design for cold store ceilings in Table 1.


Application Distributed qk (kN m-2) Concentrated Qk (kN)
Typical Design of Cold Store Ceiling 0.25 0.9
Domestic dwelling 1.5 1.4
Office light load 2.0 1.5
Office heavy load 3.0 4.5
General Storage 7.5 7.0
Inspection Scaffolding 0.75 -
Scaffold for painting and cleaning 1.5 -
Scaffold for general builderswork 2.0 -

Table 1 – Distributed and Concentrated Loads for load bearing floors in various structures


It is very evident from Table 1 that the load bearing capacity of the minimum requirement for a cold store ceiling is much less than any working space. Where there are penetrations through the insulated panel for pipes, electrical cables, sprinkler heads, ventilation or other services the mechanical integrity of the panel may be adversely affected, particularly where penetrations are grouped together. It follows that roof voids should not be considered to be working spaces unless particular arrangements have been made to ensure that the load imposed in performing the work, including accessing the place of work, is not carried by the insulated panel but is supported directly from the trusses or portal.

In modern coldstore buildings walkways for this purpose are often included in the design, but in older buildings this is less likely. If access walkways to enable work on valve stations or other equipment are to be retrofitted, whether as a temporary measure or a permanent feature, then it follows that some form of temporary structure is required during that construction work in order to avoid placing any load on the ceiling during the installation of the walkway. In many cases the only way to provide sufficient support to a ceiling panel to enable this work to proceed is by constructing a temporary support system below the ceiling to prop it up during the work. Free-standing, self-supporting cold rooms need to be assessed on a case-by-case basis to determine the level of load that can be applied in normal operation, during routine maintenance and under exceptional circumstances. Provision for temporary support may be required in some cases.

It also follows that roof voids above cold stores should not be used for storage of any material, even if it is considered to be lightweight, unless the building has been designed for storage in that area. This is very unlikely for any load imposed directly onto an insulated ceiling panel.
Services such as electrical switch panels should not be installed directly onto insulated panels. Where mineral wool panels are required, for example to provide a certain level of fire rating for the structure, permanent walkways are essential to keep all foot traffic off the panels.





Installation

Permanent damage can be done to insulated ceiling panels during the construction phase of a project, particularly at stairwell entrances and common thoroughfares. Care must be taken to ensure that panels, particularly interlocking joints and edges, are suitably protected during construction and traffic across panels is eliminated or minimised. Temporary edge protection conforming to BS EN 13374-2013 will be required while the ceiling is under construction. Particular care must be taken to ensure that an appropriate vapour barrier is installed and to avoid damage to it during fit-out as this can significantly compromise the life of the panels. If any of the weight of the barrier is borne by the insulated panel this will reduce the load bearing capability in that area so additional support may be required. Where penetrations through the panel are required, whether for refrigerant pipes or for other services such as lighting, sprinklers or electrical equipment, the aperture must be carefully sealed before the store temperature is pulled down to reinstate an adequate vapour barrier. Additional support may be required in the vicinity of the penetration to provide sufficient structural strength.


Inspection and maintenance

The Health and Safety Executive Safety Alert CON 4-2010 emphasises that ceilings should be presumed to be fragile until it is proved that they are not. It goes on to state that cold store ceiling panels should not be used as a working platform unless a suitably qualified person, for example a structural engineer, has confirmed that the panels and their supports are suitable for that purpose and are specifically designated for it.

The condition of cold store ceilings and roof voids should be inspected regularly to note any degradation and to plan for remedial action if required. Ceiling panels should be examined for signs of water damage (core samples and thermographic inspections can assist with identifying the severity of water ingress) or separation of the metal skin from the core material (delamination). Composite insulation panels derive the majority of their strength from the proper adhesion of their upper and lower steel skins onto the insulated core. When delamination of a composite panel occurs, a significant proportion of the panel strength will be lost. Any delamination must therefore be very carefully investigated. Where this is found, provision for additional temporary support, either from below the ceiling or from above, should be made as soon as possible and access to the roof void should be prevented until a safe system of work has been implemented.

The insulated panel support system, particularly the drop rods, should be inspected for signs of corrosion or lack of load bearing ability. Nylon or plastic drop rods became common in the 1970s but these have been found to be prone to failure due to weakening with age. This was a contributory factor cited by HSE in the accident that led to the issue of CON 4-2010 and has been noted as a factor in several other incidents. It is strongly recommended that any nylon drop rods are replaced with stainless steel (or equivalent) at the earliest opportunity. The same applies to drop rods supporting air coolers or other equipment in the store.

Insulated ceilings are usually supported by drop rods suspended from the structure of the building, usually a portal frame or truss. The lower end of the drop rod is attached to a pre-formed metal section, sometimes called a “top hat section” because of its shape, which provides a ledge for the edges of adjacent panels to rest on. Some older systems, particularly prior to 2000, used other support mechanisms including glued sectional insulation and timber batten supports, which are prone to failure due to ageing of these components. If the composition of the support mechanism is not known then it should be established by a detailed investigation because the support may have reached the end of its useful life.

Where ceiling voids are exposed to excessive moisture, either through rainwater ingress or as a result of condensation, the water can soak into insulated panels and will apply an additional distributed load. The water can also weaken the bond between the core of the insulated panel and the metal facing, particularly if there has been repeated freezing and thawing of the water. It may also cause corrosion of the support mechanism, particularly in older constructions. Corrosion of drop rods typically occurs 10-15mm below the top surface of the panel so close visual inspection is required to find it. Where the insulation is at a lower temperature than the surrounding air it will create a water vapour pressure gradient which draws moisture from the air into the insulation. It is therefore very important to ensure that a robust, high quality vapour seal is provided on the insulated panels, particularly at joints, and is regularly inspected and maintained in good condition.

Condensation on cold surfaces is likely if the surrounding air is stagnant, but it can be minimised by ensuring good air movement over all cold surfaces, particularly along the length of runs of insulated refrigerant pipes. The cold surfaces might be the ceiling panels, especially if they were selected on the basis of the minimum thickness that would accommodate the span, but they could also be the refrigerant pipes or the underside of the roof panels above the roof void, particularly if these have little or no insulating properties. This roof sheet will get very cold due to night time radiation and may even reach a lower temperature than the surface of the insulated panels below it. This is particularly likely in older buildings but it is not an issue if the roof panels conform to the current building regulations. It may not be possible to eliminate condensation completely on cold pipes, particularly when the external humidity is high, but the condensate must not be allowed to accumulate or left to lie on top of insulated panels. It may be beneficial to add some form of air heating to the roof void, but heating without adequate air movement is not a solution as it will just cause the moisture to recondense on the cold surface.

When a low temperature cold store is turned off and warmed up, either due to equipment failure or to effect a change of use to chill or ambient storage, an inspection of the condition of the ceiling panels should be completed before the temperature starts to rise. If the panels have become icebound there is a risk that they will lose their structural strength if the ice is allowed to melt. Even if the support structure has carried the additional weight of the ice it might not be able to cope with the lack of rigidity produced by melting the ice within the panel.


Other Safety Considerations

Access to the void spaces above cold stores should be by a permanent stairway. Ladders are less preferable because they do not accommodate the tools and equipment that are routinely required in order to carry out maintenance. If ladders are used, they should be permanently fixed with a suitable cage and with appropriate landings or rest platforms not more than 6 m apart if the vertical rise is more than 9m. The area at the top of the ladder for transfer to the roof should be robust and secure. The base of the ladder must be kept clear of obstructions including temporary storage and fork lifts or pallet trucks. Edge protection, also robust and secure, must be provided where there is any danger of personnel falling over the edge. The protection should be strong enough to withstand a person stumbling and falling against it. Care should be taken with changes in height of the ceiling, particularly if the drop is more than one step, in which case edge protection should also be provided at the change of height. Lightweight covers over voids and edges should not be used as these can be difficult to see and may be indistinguishable from the ceiling panel once they are dirty. Likewise the personnel protection should not rely on taped markings to delineate hazards as these can also be masked by dirt or dust and can also be scuffed or removed. Loading criteria for edge protection is included in BS EN 1991-1-1:2002 and BS EN 13374:2013. Note that the insulated panels are not structural elements so edge protection needs to be secured to the main building structure, incorporated into a suitably secured walkway or a self-supporting counterbalanced guardrail tested to BS EN 13374:2013 Class A.

The Construction (Design and Management) Regulations 2015 place requirements on duty holders to provide information on the load bearing capability of the structure, including safe means of access to heights, and to design out the risk of falls at the planning stage of a project.

The Work at Height Regulations of 2005 also apply. Although not specifically mentioned in the 2005 Regulations it is necessary for employers to ensure that their employees are fit to undertake work at height. This is covered by regulation 6 (Health Surveillance) of The Management of Health and Safety at Work Regulations 1999 which states that employers shall ensure that their employees are provided with appropriate health surveillance in consideration of the risks identified by the risk assessment required by regulation 6 of the 2005 Regulations. Such a health check might include checks of hearing, vision, grip strength, lung function, body mass index and a musculoskeletal assessment as well as specific checks for diabetes, epilepsy or other conditions that might cause a sudden loss of consciousness. Regulation 13 (Capabilities and Training) of the Management of Health and Safety at Work Regulations 1999 places a further requirement on employers to ensure that employees undertaking works are capable of doing so safely. Assessment of capability includes consideration of training, experience and physical fitness.


Recommendations

For new facilities it is recommended that suitable permanent access is incorporated into the design of the roof void to ensure that all equipment that requires maintenance, even on an intermittent basis, can be accessed on permanent walkways without the need to walk on suspended insulated panels. Alternatively, the ceiling should be designed as a floor (rather than a ceiling) using appropriate materials with a suitable load bearing capacity based on the expected activities. Note that composite insulation panels are not suitable for this purpose as they will delaminate if subjected to regular cyclic loading.
For existing facilities consideration should be given to the incorporation of permanent walkways before the condition of the ceiling deteriorates to such an extent that it creates an immediate danger. This incorporation work would probably require the ceiling to be temporarily supported from below for the duration of the work. Access to roof void areas that are not served by walkways should be severely restricted and when it is necessary temporary measures such as support from below should be put in place to reduce the risk of an overload condition occurring.
It is recommended that the roof void is inspected for moisture at least once per month and a tension check of drop rods is completed every six months to ensure that they are all still bearing load. The root cause of any loose rods should be investigated thoroughly as it is possible that this is caused by the ceiling sagging in another part of the store resulting in additional load imposed on some other rods.

It is recommended for buildings less than 20 years old that an annual inspection by a competent person is documented and a comprehensive survey is conducted by a structural engineer or insulated envelope designer every 5 years to confirm the integrity of the structure. The report should include design drawings, sketches and records of the materials of construction and the condition of the panels and the support mechanism. It should include a thermographic scan of the panels and the support mechanism and a sample intrusive examination of the support mechanism hidden within the insulated panels. The survey report should contain a statement on acceptable loading for the ceiling, ranging from confirmation that the original design load (If known) is still acceptable to notification of “zero loading” which would prohibit access to the roof void area.
In older buildings it may be appropriate to conduct the comprehensive survey more frequently, for example instead of the annual inspection every second year.

If significant changes to the condition of the ceiling are identified in the annual inspection or at any other time then access should be prohibited and a comprehensive structural survey commissioned to establish the condition of the fabric and the extent of remedial work required.

For further information refer to


Disclaimer
The Institute of Refrigeration accepts no responsibility for errors and omissions.
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Editor: Amanda