Dear AMMRL,
Thank you very much to responders to my query, the replies were really excellent and have been of enormous help. I hope that the summary of replies I have put together below is similarly of help to others. If any one wants the info in a word file, please send me a request.
Concerns and precautions for impending construction work
Compiled by Karel D. Klika with a great many thanks to the following contributors: Monika Ivancic, Ryan McKay, Bob Berno, Goran Schomer, Uwe Langer, Mark Swanson, Martha Morton, Heather Schenck, Gerado Cedillo, Joe Dumais, Mike Strain, Clemens Anklin, and Karen Ann Smith.
1. Vibrations
What can happen
The amount of vibrations that the machines are subjected to can easily, and often does, exceed what the anti-vibration measures that are in place (e.g. pneumatic dampers) can compensate for. Vibrations can be catastrophic for spectra, and lead to a lot of additional work to re-run spectra.
Things to consider
How much of a problem is experienced depends on factors such as the distance between the construction work and the location of the magnets and the type of ground (rock, hard clay, soft soil) as well as the type of demolition/construction work involved, e.g. explosives, collapse of large building segments (intentional or otherwise), pile driving, jack hammering, and pounding of foundations.
Consequences
a) Spectral acquisitions during the work time can easily be rendered unacceptable, or at least of much poorer quality than usually obtained. Of course it is very much dependent on what spectra are being acquired, so it can make sense to acquire less sensitive spectra during the work time and more demanding spectra outside of work hours. Or re-run spectra, e.g. quick protons just to see if a reaction has occurred during the day so one can move on, then run a better spectrum later if need be. Autosamplers are likely to be highly beneficial in this context.
b) Chronic exposure to excessive vibrations can lead to material fatigue and damage to the magnet. Damage to a magnet costing tens of thousands of dollars (50k) to repair has been reported. In the extreme, magnet quenching is conceivable and/or the complete write-off of the magnet.
c) Acute shocks, however, would need to be extreme to cause damage to the magnet and are unlikely to occur as a result of construction work. Magnets have even been known to survive earthquakes.
Precautions
a) Accelerometers (installed at one’s own expense or taken up by the construction company) can be installed to monitor the exposure to vibrations and provide legal proof in the case of prior agreed-to vibration limits being exceeded. It is worth finding out what the tolerances are for the magnets in question, limits might be, for example, 0.1 g for vertical displacement and 0.05 g for horizontal displacement. Tolerances are presumably not for chronic exposure, and nor do they take into account the age of a magnet.
b) It can be worth considering hiring vibration consultants.
c) Otherwise, there is not much one can do aside from relocating the magnets to really ensure there are no problems or try to block the use of really detrimental building methods.
Vibration issues are probably the greatest problem created for magnets by nearby construction work. They are great in terms of their potential effects on magnets, and consequently on spectra, but also in terms of viable solutions. Communication is key, from the architects and directors of the building/demolition companies all the way down to the project managers to find out what will be done (and when) and what building methods will be employed. Agreements need to be reached on what the vibration limits are, whether to install accelerometers, what to do in case of damage, what to do if limits are exceeded (e.g. immediate shutdown of construction equipment), and what construction methods will be employed.
2. Disturbance to the magnetic field
What can happen
The field changes and homogeneity losses can be catastrophic for spectra, and can lead to a lot of additional work to adjust the shim and/or re-run spectra. But the situation is very dependent on not only what the disturbances are, but what is being run – spectra with high demands for homogeneity, locked/unlocked, etc.
Things to consider
How much the stray field of the magnets extends into the work area and what entry into the stray fields will be made by large machinery.
Consequences
a) Spectra acquired during working hours when machines are running or large equipment is being moved around can easily be rendered unacceptable, or at least of much poorer quality than usually obtained. How badly results are affected is also dependent on whether spectra are run locked or unlocked. Thus it is a question of both field stability and homogeneity and what the spectra are prone to, one or other or both. Since it is very much dependent on what spectra are being acquired, it can make sense to acquire less sensitive spectra during the work time and more demanding spectra outside of work hours. Or re-run spectra, e.g. quick protons just to see if a reaction has occurred during the day so one can move on, then run a better spectrum later if need be. Autosamplers may be beneficial in this context.
b) Whilst no one has reported the need for cryoshimming, some have reported very heavy demands for shimming, e.g. trouble shimming; frequent re-shimming to get good shim settings; and re-shimming overnight, sometimes to no avail even with sophisticated shimming routines. Thus, even spectra run out-of-hours can also be compromised. How often this occurs depends on the frequency of large disturbances to the magnetic field.
Precautions
a) Extreme precautions include Faraday cages and iron shielding, but these are expensive and disruptive solutions (building work + removal of magnets) and depending on the length of the building work, not likely to be a viable solution.
b) Mapping of the field is helpful to know when problems might occur and to also possibly avoid them, e.g. not placing cranes or other heavy equipment in certain areas. This may entail actually physically marking it out or better, cordoning off the stray field limits. What field lines to mark out ? For safety, the 5 G line; for disturbance to the magnetic field, maybe the 0.5 G line for a balance between pragmatism and excessiveness.
c) It can be worth considering hiring magnetic field consultants.
d) Otherwise, there is not much can one do aside from relocating the magnets to really ensure there are no problems.
Disturbance to the magnetic field is probably the next greatest problem created for magnets by nearby construction work. They are great in terms of their potential effects on spectra and invalidating shim settings, but also in terms of viable solutions. Again, communication is key, from the architects and directors of the building/demolition companies all the way down to the project managers to find out what will be done and when. Extreme precautions include installing Faraday cages and iron shielding, both of which can be beneficial after completion of the construction work but may be unnecessary in either phase.
3. Dust and dirt (and ferromagnetic particles in particular)
What can happen
A great deal of dirt and dust can invade the NMR room, either through the air or via foot traffic, and wreak havoc with consoles and magnets. Magnets can collect ferromagnetic particles which can be produced in abundance from construction work.
Things to consider
How much of a problem dust and dirt are likely to be are dependent on whether the construction/renovation work is inside the building or not and what the access ways to the NMR unit are like if the building work is away from the building housing the NMRs or even adjoining it.
Consequences
Disruptions to the consoles and to the magnets which may be rendered inoperable. Ferromagnetic particles are impossible to remove from an active magnet and costs associated with removal (de-energizing the magnet, removal of the inner bore) are sizeable.
Precautions
A range of possibilities:
a) At the entrances to the unit and/or NMR rooms, sticky mats can be installed and which should be changed regularly.
b) Sweeping with magnetic nail sweepers in the halls and entrance ways leading to the NMR rooms.
c) Installing an air lock to the entrance of the unit, or completing sealing off the NMR rooms as per asbestos removal methods and applying positive pressure, or using the HVAC system to create positive pressure in the rooms with filtered air.
In principle, dust and dirt should be relatively easy to deal with in most scenarios, if extremely bothersome and requiring a high workload and possibly also some significant cost. Planning well ahead of time and setting things in place can ease this problem.
4. Disruption of utilities and services
What can happen
The power, water, HVAC, or gases can be interrupted without warning either intentionally or accidentally. Even with prior arrangements for notification, this can still happen, or happen earlier than arranged. Long delays in regaining any of the services is also a concern.
Consequences
Unexpected power loss can cause problems for consoles and computers and can of course lead to loss of spectra under acquisition and/or data.
Precautions
a) Planning and communication are the essential requirements. Two problems seem to be impatience on the behalf of workers, e.g. shutting off a utility earlier than indicated, and the assumption that since it is late at night or on the weekend and nobody is around, that it is alright to shut off a utility. This aspect is worth emphasizing.
b) Setting up of communication channels for intended and planned shutdowns but also in the event of unintended shutdowns or a change in plans.
This should seemingly be one of the easiest problems to deal with but there are enough anecdotal stories to counter this assertion. Usually building maintenance departments are very good with notifications of disruptions to utilities and services, but they cannot of course account for unintended disruptions or lack of notifications. Again, communication is key with the project managers to find out what will be done and when and to continue this all the way down to the subcontractors, tradespeople, and the workers at the frontline.
5. Worker access to the facility/entry into the field which may extend out of the facility and associated dangers
What can happen
Unauthorized or entry with disregard for guidelines has caused damage to magnets (even complete loss of a magnet in one story from last year) and injury to people due to pacemakers, prosthetics, or objects turned into projectiles. On the other side, the personnel running the facility are obligated to make sure that people are informed, and this applies not only to the NMR room, but if the stray field extends outside of the room and into the work area or access ways.
Things to consider
a) Who has entry and access.
b) Should workers always be escorted.
c) Access of tools and machinery within the facility or within the stray magnetic field.
d) Use of tools and machinery within the facility or within the stray magnetic field.
e) Process of informing workers.
Precautions
a) Map the magnetic field, know where it is, what it is a danger to and to whom (pacemakers, tools), what is a danger to it. This should entail actually physically marking it out or better, cordoning off the stray field limits. What field line to mark out ? For safety, the 5 G line is generally considered the safe limit (for disturbance to the magnetic field, maybe the 0.5 G line for a balance between pragmatism and excessiveness).
b) Communication is the essential requirement. One important point to note is that workers need to made aware that magnets are always at field, even if the power is off.
This should also seemingly be one of the easiest problems to deal with but there are enough anecdotal stories to again counter this assertion. As always, communication is key, from the project managers all the way down to the subcontractors, tradespeople, and those actually doing the work.
6. Miscellaneous points
Some small, but obviously important things to remember and take care of, are:
a) Access for cryogens has to be maintained.
b) If protecting magnets with plywood boarding, access for cryogen filling, changing samples, probes, etc. needs to be maintained.
7. Final comments
Endless and informative communication, thorough and meticulous planning, and enormous amounts of work are required to minimize disruptions and avoid major catastrophes. Communication is vitally important, with project managers, subcontractors, and workers. It is necessary to stress repeatedly that the instruments are extremely sensitive, very expensive, have strong magnetic fields (even when there is no power), and utilities cannot be turned off without prior notification. Sentinel attention is paramount, particularly with workers who come into close vicinity to the magnets, both for their safety as well as for the magnets. Sometimes the best solution can be to move the magnets to a safe place, either for continued use or for mothballing. With vibration issues, even with mothballing, magnets may still require relocation. Legal issues need to be sorted out prior to the start of any building work, and some of the points raised here should involve legal arrangements being put in place.
Thanks again.
Regards,
K. Klika
Received on Sun Jan 14 2018 - 23:28:53 MST