Gowned lab worker under hood w TV2 on Wall

Clean Room Design & Build


Industrial Applications
Process Classification
Aerospace ISO Class 5-7
Assembly of Touch Screen ISO Class 7
Composite Materials ISO Class 8
General Industrial ISO Class 8
Injection Molded Parts ISO Class 7-8
Optical ISO Class 5-7
Process Classification
Semiconductor ISO Class 5
SMT Assembly ISO Class 7-8
Solar ISO Class 5-7
Wafer Board ISO Class 5
Consumables and Pharmaceuticals
Application Classification
E-Liquid ISO Class 7-8
Food Packaging No Classification
Nutraceutical Packaging ISO Class 7-8
Pharmaceutical Compounding ISO Class 7
Pharmaceutical Packaging ISO Class 8
Sterile Compounding ISO Class 5
Medical Devices
Application Classification
Device Reprocessing ISO Class 7
Inplantable Devices ISO Class 5
Medical Device Packaging ISO Class 7-8

Building and designing a cleanroom requires proper planning, and a thorough understanding of the equipment and technology used in the controlled environment to ensure it’s correct and safe operation. Clean room design will be heavily dependent on the type of process that will be carried out in the space chosen.

Many companies prefer to consult with an engineer, an architect, an HVAC specialist and a general contractor before moving forward with a particular clean room design.

For the purposes of this article, we’ll get right down to the basics of best practices for optimal clean room design.
























ISO 14644-1 Cleanroom Standards
Classification Maximum Particles/m3 FED STD 209E Equivalent
≥0.1µm ≥0.2µm ≥0.3µm ≥0.5µm ≥1µm ≥5µm
ISO 1 10 2.37 1.02 0.35 0.083 0.0029
ISO 2 100 23.7 10.2 3.5 0.83 0.029
ISO 3 1,000 237 102 35 8.3 0.029 Class 1
ISO 4 10,000 2,370 1,020 352 83 2.9 Class 10
ISO 5 100,000 23,700 10,200 3,520 832 29 Class 100
ISO 6 1.0 x 106 237,000 102,000 35,200 8,320 293 Class 1,000
ISO 7 1.0 x 107 2.37 x 106 1,020,000 352,000 83,200 2,930 Class 10,000
ISO 8 1.0 x 108 2.37 x 107 1.02 x 107 3,520,000 832,000 29,300 Class 100,000
ISO 9 1.0 x 109 2.37 x 108 1.02 x 108 35,200,000 8,320,000 293,000 Room Air
Exterior view of hospital

Seattle Children’s Hospital: Preventable Disaster?

In May 2019, Seattle Children’s Hospital faced an emergency situation where 14 surgical rooms were forced to cease operations, with over 3,000 families potentially affected by deadly Aspergillus mold exposure. The Seattle Children’s hospital was forced to move or reschedule over 1,000 surgeries. Unfortunately, one patient recently died in 2018 after developing an infection as a result of exposure to this type of mold. Many more could face ongoing health complications.

How this could happen in this modern age of technology, to a hospital which, in 2019, U.S. News & World Report named one of the 10 best children’s hospitals in the country? In fact, U.S. News & World Report has recognized Seattle Children’s as a top children’s hospital every year since it began ranking medical facilities more than 25 years ago.

The looming question is “Was this tragedy preventable, and, if so, what should have been done?”

Who’s at fault?

According to the Centers for Disease Control and Prevention, Aspergillus is a common mold found both indoors and outdoors. Unless you live in a cleanroom or isolation room, you have most likely inhaled millions of it’s spores into your lungs every day since your birth.

While most people breathe in these spores every day without getting sick, the mold poses a real risk to those with compromised immune systems or lung disease. Mold growth can be accelerated and concentrated in man-made surroundings whereas in natural environments, the concentrations are diluted to just a few parts per million by global atmospheric conditions.  The way to prevent these spores inside closed spaces like operating rooms and patient rooms inside hospitals is to carefully monitor pressure, temperature and humidity.  As long as temperature and humidity are maintained a proper levels mold can not grow and if positive pressure is maintained the spores will, for the most part, be kept outside the area.

Aspergillus, and mold in general, can cause allergic reactions and infections in the lungs and other organs in the body. This is precisely why hospitals must monitor and manage mold growth of any type – patients in the hospital (children and elderly) are already at a greater risk for adverse effects of mold growth; even more so if they have existing health complications and compromised immune systems.

With that said, the Seattle Children’s Hospital had known deficiencies in room air purification systems. The patient who recently died (2019) contracted the Aspergillus mold infection a year ago.  That was known at the time and should have been a wake-up call to install equipment to monitor conditions to prevent a re-occurrence.  It is unclear which, if any, preventative or remediation processes were put in place after the first known incident. It is known, however, that they were largely ineffective in preventing further growth; the mold was still present a year later.

Ultimately, the Seattle Children’s Hospital is at fault – mold and other potentially harmful pollutants, of natural or synthetic origin, must be controlled no matter the cost.

What could have been done

There are dozens of monitoring systems available to hospitals, and some even provide advanced alerts when relative humidity and temperature levels become ideal for mold growth. These systems can allow for immediate correction of dangerous conditions.  An alert delivered in a timely manner can help maintenance personnel make adjustments to the HVAC systems and initiate clean-up measures to get rid of the mold.  Carefully monitoring potentially contaminated areas is a must for every health care provider.

Experts agree that having multiple environmental monitoring systems in place is a good idea; one tied in with a building management system, and another stand-alone as a fail safe. It is also important to note that any system which requires an employee to physically view a monitor or screen can only be as effective as the person viewing it. A better alternative is a system which includes a digital display of current values, offers a room or local alarm system when level are outside set ranges, and has the ability to notify key personnel via SMS, email and/or automated phone calls when issues of air quality occur. Many of these systems are specifically designed for hospitals, and include options to monitor both negative and positive pressure isolation rooms – helping to reduce exposure to mold and cross contamination.

Although there are only a handful of manufacturers that offer such comprehensive systems, they do exist, and are a fraction of the cost of having an incident like the one at Seattle Children’s Hospital. In fact, if you look at the math, a hospital could buy a comprehensive monitor for about the same cost it takes to operate a surgical room  – for 7 minutes.


Bottom line, there are no excuses. Hospitals operate on a tight budget, and have ongoing issues with accounts receivables from patients and insurance carriers. There are huge fees to surgeons, malpractice insurance, and other costs to operate a modern and efficient hospital.  However this is no excuse for overlooking something as basic as providing a mold free environment.  A piece of equipment as inexpensive as a modern advanced monitoring system to prevent mold growth and provide critical data on the health of the environment.  This solution does and will continue to have a huge impact of patient health and the ability to recover from surgery and the issues that brought the patient to the hospital in the first place.


Large pix of ddi

2di sensors

Sensors used with the TV2 monitors are of two different types:

  1.  Wired sensors for TV2-202 monitors
    1. DD1 Temperature only (-40°C to 120°C)
    2. TSMRH3001 Temperature/humidity (-20°C to 80°C, 5% to 90%)
    3. WDP2 Differential pressure sensor (±0.5″wc)
    4. TC-x Thermocouples (200°C to 1250°C, type dependent)
  2. Wireless Sensors for TV2-201 monitors
    1. WS4HETM External Thermistor (-30°C to 80°C)
    2. WS4HITMIHM Temperature/humidity (-20°C to 80°C, 5% to 90%)
    3. WS4HTC-x Thermocouples (200°C to 1250°C, type dependent)

All sensors designed to work with the TV2 monitors are digital.  This means that each has an analog to digital converter built into the sensor, so technically the sensors take readings as an analog sensor but the signal is converted to a digital value before being transmitted to the TV2 monitor.  This is important because when a digital signal is transmitted via a direct wire it is much more unlikely to be affected by noise generated by the external environment.

We make every effort to insure that all 2di sensors meet or exceed the accuracy requirement necessary meet all regulatory and industry standards that apply to their intended uses.  For example, many of our customers use the TV2 sensors to monitor, log and alarm refrigerators and freezers storing vaccines.  The CDC as well as certain industry groups such as JCAHO, recommend that temperature sensors used to monitor refrigerator and freezer temperatures have an accuracy of at least ±0.3°C.  All of our temperature sensors except thermocouples, which are used for extreme temperature not necessary for vaccine storage, meet or exceed this level of accuracy, (see table below).

  1.  Wired sensors for TV2-202 monitors
    1. DD1 Temperature only (±0.30°C)
    2. TSMRH3001 Temperature/humidity (±0.3°C, ±1.5%)
    3. WDP2 Differential pressure sensor (±0.002″wc)
    4. TC-X Thermocouples (t-type ±1.0°C, E, J, K types ±2.2°C)
  2. Wireless Sensors for TV2-201 monitors
    1. WS4HETM External Thermistor (±0.3°C)
    2. WS4HITMIHM Temperature/humidity (±0.3°C, ±1.5%)
    3. WS4HTC-x Thermocouples (t-type ±1.0°C, E, J, K types ±2.2°C)

What role does the TV2 monitor play in sensor accuracy.  The TV2 monitor whether the TV2-202 or the TV2-201 does have a very small impact on the 2di sensors, but it is in the range of 0.1% of the reading.  This means that it could affect the sensor accuracy by that amount, so a DD1 sensor could by ±0.3001°C.  This amount is so small that it can not be measured except with an extremely accurate scientific instrument and is within the limits prescribed by CDC, FDA, JCAHO, and other certifying agencies.  This means that if sensors are re-calibrated by 2di it is not necessary to send the TV2 monitor with the sensor.

How often do sensors need to be re-calibrated?

DD1 – Never needs to be re-calibrated, however some certifying agencies require sensors to be re-calibrated every year or two.  We generally put a date two years in the future on our calibration certificates as the re-calibrate date.

TSMRH3001 – Never needs to be re-calibrated. Under normal operation, the sensor may drift to ~0.1%RH/year. We qualify the HS3001 for 10years operation.  The temperature part of this sensor also has minimal drift.  We put a date two years in the future on our calibration certificates as the re-calibrate date.

The re-calibrate date listed on 2di Calibration certificates is listed because most certificating agencies want to see a re-calibration date and a two year re-calibration date seems to make them happy.  We could put a date of 5 years for re-calibration certificate but the agencies would balk.  They do not yet grasp that modern digital sensors if manufactured correctly, do not drift so they really never need to be calibrate.  The exception to this is thermocouple sensors which do drift over time.