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SGA's 95 Greene Street in Jersey City, NJ uses vibration control techniques
SGA's 95 Greene Street in Jersey City, NJ
Robert Benson

How to Plan for Vibration Control in Lab Buildings

How to build low vibration, flexible laboratory buildings that cater to the life sciences market

With demand for flexible lab buildings on the rise, the importance of strategic lab planning has never been greater. While there are many factors that play into the lab design process, one of the most critical elements to plan for is vibration control.

95 Greene Street, the first lab-ready life sciences property in Jersey City, NJ, employed vibration control strategies to protect research within the labs. Project by SGA
The design of 95 Greene Street, the first lab-ready life sciences property in Jersey City, NJ.
Robert Benson

Vibration—the periodic back-and-forth motion of the particles of an elastic body or medium—happens everywhere, and is oftentimes below the threshold of human perception. However, this natural phenomenon has a major impact on lab testing and processes and can even dramatically alter the outcome of scientific experiments, making it a critical but sometimes overlooked component of lab design. This is because common lab equipment like high-resolution microscopy, microscopes, PCR machines, incubators, and 3D printers are highly sensitive to vibration, which can be caused by a number of internal and external factors. 

Internally, floor vibrations from foot traffic, elevators, HVAC, fans, and air handling systems play a significant role in lab vibration while external elements like road traffic, railroad proximity, and nearby construction sites can also cause an impact. Essentially, the extent to which vibration can be minimized throughout the building will ultimately influence the success of the research.

But, to understand how to control vibration, it is important to first understand how it actually works. While vibration is the oscillation of something, examining how it oscillates, in terms of the frequency and velocity of the vibration, is key to determining how to control it. 

Frequency is simply how much time it takes to go from one place to another, and back, like a lap. In terms of vibration, this is described as the number of laps the vibrating medium accomplishes per second. Measured in Hertz, one lap per second is 1 Hertz,1,000 laps per second is 1,000 Hertz, or 1 Kilohertz. The units are abbreviated as 1 Hz, 1 Khz, 1 Mhz, and so on.

While understanding vibration speed is important, it is only the first step. The next is determining how much the medium is vibrating. More specifically, identifying how much energy the vibration carries will reveal the amount of energy it has to impact the lab building. Therefore, we talk about a quantity called the “root mean square velocity,” abbreviated “RMS.” The higher the RMS number, the higher the likelihood that the interior elements or composition of the building will vibrate. 

Further, a single object can vibrate in more than one way at the same time. At 1Hz, it can vibrate very little; at 100 Hz, it can vibrate a lot. Take music, for example: a high-pitch violin note could vibrate in the air at 10,000 Hz, while a low bass singer could also vibrate in the air at 100 Hz. Both can be heard at once. Much in the same way, the floor in a building could be vibrating at both frequencies at the same time. In fact, in real life, everything is vibrating to some extent, at every frequency, all the time. The question lies in how much.

Floor vibration in buildings is often described in micro-inches per second or micrometers per second. This refers to the RMS velocity figure, but without frequency information, only a fragment of the picture is shown. Is the floor vibrating at 8,000 mips at 100 Hz, but perfectly still at 10,000 Hz? Is it vibrating at 8,000 at all frequencies? Without frequency information, there is no way to determine the scope of the vibration. Instead, the full spectrum needs to be shown. This is a graph that shows the RMS velocity of the vibration for a hypothetical floor, at various frequencies.

chart 1 on vibration control by SGA
SGA

Note that “micro-inches per second” is often abbreviated “mips” but more properly written “μin/s.” If the metric system is used, the relevant unit would be “μm/s.” In the example above, the floor is vibrating at almost 10,000 μin/s at 8 Hz but only at 10 μin/s at 80 Hz.

However, not every project comes with a vibration spectrum graph. So, how can this be shown without having to draw one? 

In the 1980s, Eric Ungar and Colin Gordon faced similar obstacles, and developed what is now known as VC (Vibration Criteria) curves. These are a set of ready-made lines on a graph that can be used to easily describe vibration with abbreviations like “VC-D” without the need for a spectrum or a table. They also incorporate ISO standards for vibration in various space types.

chart 1 on vibration control from SGA
SGA

Notice that the floor vibration in this example is just barely below the “Residential Day (ISO)” line at its highest point, which means that this floor is suitable for an apartment but not for an operating room (or a sensitive lab!). Less vibration is always better for science.

Although, in determining the suitable vibration levels for labs, it is important to note that different science activities have different vibration standards.

The most common vibration-sensitive activity in a lab is optical microscopy – or examining things through a microscope. Naturally, when looking at very small things, shaking the table makes it hard to see. The crucial question here is: just how much shaking will make it too hard to see?

Fortunately, Colin Gordon and Bassett Acoustics produced an excellent reference work1 that relates various levels of magnification to acceptable vibration limits. The table below is adapted from their paper. Note that the vibration limits are maximum allowable, meaning that measured vibration must be less than these levels.

Magnification

Vibration Criteria

Comments

100x or less

Operating Room (ISO)

Flat portion of line at 4,000 μin/s

400x

VC-A

Flat portion of line at 2,000 μin/s

1000x

VC-C

Flat portion of line at 500 μin/s

Much of modern biological science involves modifications or additions to an optical microscope, which enables enhanced imaging or actual scientific work conducted under a microscope. These alterations substantially increase the sensitivity of the microscope. The paper described above gives values for some examples of these activities.

Activities

Vibration Criteria

Comments

Digital Imaging

Fluorescence

VC-C

Flat portion of line at 500 μin/s

Microinjection

Micromanipulation

Electrophysiology

Confocal Microscopy

VC-D

Flat portion of line at 250 μin/s

It would be impractical to provide VC-D throughout the whole floor plate, though every building designer and owner wants to provide maximum flexibility to accommodate future science. So, how can a whole building be planned?

Fortunately, most labs only need a few areas of low vibration to support a few microscopes (it is rare to see a microscope on every lab bench). This allows for the creation of microscope-suitable spaces without extending the low-vibration area to the whole floor plate. For this, there are two major tools that can be utilized: 

  • Microscopes can be placed on pneumatic tables, whereby tabletops float on a piston filled with compressed air or nitrogen. These work just like shock absorbers in a car, and generally cut about 90 percent of the vibration from the floor. Because the lines on the vibration criteria are logarithmic, where each is 10 times the one previous, the 90 percent reduction from such a table can improve conditions by one whole criteria (for example, from VC-B to VC-C).
  • Floor structure is not homogenous. At the center of a structural bay, far from any column, the floor can vibrate significantly. Directly next to a column, it is very unlikely that the floor will vibrate as much. In general, locating a microscope near a column can improve vibration by another whole criteria step (for example, from VC-C to VC-D).

Each of these two techniques attain one criteria of improvement (that is, cut vibration down to 1/10th of what it was before). Together they achieve 1/100th of what there was before, or two criteria.

So, how is the right vibration target for a building determined without knowing the kind of lab that will be inside it? Imagine an optical microscope being used at 1,000x magnification, located on a pneumatic table, next to a column. In this case, a high-spec but still common microscope is being considered, located using both techniques previously discussed. 

  • The microscope must sit on a surface which is VC-C, per the table above. That is the top of the pneumatic table. 
  • That means the floor under the table has to be at least VC-B, since the table improves vibration by about one “step.” 
  • If the floor right next to a column is VC-B, then a worst-case spot in the middle of a structural bay can be VC-A.

This process reveals that VC-A, which is at about 2,000μin/s above 8 Hz, is a safe baseline criterion for a laboratory building.

Note that this example started with a very high-end optical microscope. It is also common to assume that this type of optical work would be done on the ground floor, or a specially reinforced area of structure, and instead use a microscope operating at around 400x or 600x as a baseline. In that case, the ISO standard for operating rooms (4,000μin/s above 8 Hz) would be sufficient as a general baseline. In fact, 4,000μin/s is often quoted as a figure for lab building planning.

The table below summarizes what work is possible for different baseline criteria.

 

Microscopy Type

 

Building Baseline

(Vibration in center of structural bay)

ISO Operating Room

(4,000μin/s above 8 Hz)

VC-A

(2,000μin/s above 8 Hz)

100x or less

On pneumatic table or near column

Anywhere

400x

On pneumatic table and near column

On pneumatic table or near column

1000x

Special construction required

On pneumatic table and near column

Digital Imaging

Fluorescence

Special construction required

Special construction required

Microinjection

Micromanipulation

Electrophysiology

Confocal Microscopy

Special construction required

Special construction required

In the table above, “special construction” can mean several things:

  • The ground floor with a concrete slab sitting on the earth. This generally vibrates a lot less than upper floors.
  • Deeper structural beams. The depth of beams reduces flexing, which also reduces vibration energy (the RMS value). 
  • Specialty active vibration cancellation feet or tables. These are tiny motors, controlled by a computer that vibrates in a way that offsets the floor vibration to produce a steady surface. This is effective but it isn’t cheap!

Of course, these are only general rules. There are many other factors, including the location of stairs, elevators, mechanical rooms, and perhaps most importantly, beam span length. Every individual science task is likely to have slightly different requirements, too.

It’s also important to remember that vibration isn’t just one number; the whole spectrum needs to be considered. VC curves are a good way to do that. Further, VC-A is a very good baseline target for lab buildings, but the ISO operating room standard can work as well.

Armed with this knowledge, low vibration, flexible laboratory buildings that cater to the life sciences market can be built. In doing so, this will further safeguard the costly research efforts of life sciences companies, creating an even stronger, science-forward future. 

REFERENCES

  1. http://www.sandv.com/downloads/0702amic.pdf

Matthew Fickett, AIA, CPHC, LEED, is principal at SGA.