Several news stories have hit the headlines lately regarding ozone exposure incidents. For the most part, these have involved contractors or employees that were not directly involved with the use of ozone at these facilities. In other words, the individuals exposed were not familiar with the basics of ozone safety, but they were exposed to ozone nonetheless.
While these incidents can certainly become overblown by mainstream media (as media will do), that makes them no less significant to the ozone industry – it is public perception that counts. Where truth and media coverage collide, media coverage always has the upper hand. The matter is complicated further when ozone exposure incidents lead to civil suits – miring ozone-use facilities and ozone manufacturers in substantial legal expense and additional bad publicity.
Unfortunately, it is possible that these recent incidents could have been avoided if more care had been given to proper ozone detection equipment and proper ozone safety procedures. Whether you have a facility using ozone or are a manufacturer producing ozone systems, this is a lesson that needs to be taken to heart.
OSHA requirements dictate that ozone levels cannot exceed 0.1 ppm, so for the sake of expense many organizations implement a single monitor to satisfy the regulation. As applications for ozone increase, however, the number of individuals that work in the vicinity of ozone systems will also increase. While the increasing number of individuals does not increase the likelihood of an ozone leak, it does increase the likelihood of exposure if a leak does occur. For that reason, the extent of ozone safety equipment and training at a facility should instead be based on the likelihood of exposure – not just OSHA regulations.
What does this mean, exactly? Take these examples:
At a small company where all employees are familiar with ozone and fully trained in the use of their ozone system, a single or small number of monitors may be sufficient for employee safety. (As always, this also depends on proper maintenance, adherence to proper procedures, etc.)
At a large company, there may only be a handful of employees that use an ozone system and are familiar with its use. These organizations should implement additional ozone monitors and safety signage in any area where “non-ozone” employees may be present. This helps ensure that all employees in all areas can remain safe and act appropriately in the event of an ozone leak.
Public facilities need to take their safety measures one step further. In a facility where the general public could be exposed to an ozone leak, all areas need to be monitored (with redundancy where possible), proper maintenance should be observed, ventilation should be present, ozone equipment rooms should have limited access and staff should be trained in how to handle an ozone leak.
Regardless of how careful a company is, ozone leaks are a reality. As users of ozone equipment, please keep this in mind as you plan your ozone systems and then communicate your safety requirements to us as we help with the design process. As a manufacturer, Ozone Solutions will continue asking questions to ensure that the equipment we sell is being sold with proper detection equipment installed. Together we can help the ozone industry continue its stellar record of safety for another 100 years.
To sum up our ongoing series comparing ozone detection technologies, here is a full list that summarizes the advantages, disadvantages and common applications for various ozone monitor technologies. For further information, visit the Ozone Monitor Technology Comparison page on our website and then browse our product pages for details!
Electrochemical Ozone Sensors
An electrochemical ozone sensor uses a porous membrane that allows ozone gas to diffuse into a cell containing electrolyte and electrodes. When ozone comes into contact with the electrolyte, a change in electrochemical potential occurs between the electrodes causing electrons to flow.
In “zero air”, little or no electron flow occurs. As the presence of ozone increases, the electrical signal increases proportionally. The monitor interprets this signal and displays the ozone concentration in PPM (parts per million).
Good repeatability and accuracy
Very quick response time (1-2 seconds)
Long battery life
Can measure ozone accurately up to 20 ppm
Moderate resistance to interference
Humidity can affect sensor
Sensitive to EMF/RFI
Limited sensor life (12-18months), even if in storage.
Less accuracy at low ozone levels (below 0.1 ppm)
Personnel (portable) safety monitoring (esp. long shifts)
Ozone Leak Detection
Stationary ozone monitoring
Ozone Monitoring & Control
Semiconductor-Based Ozone Sensors
Heated Metal Oxide Sensor Cell (HMOS)
Gas Sensitive Semiconductor (GSS)
A heated metal oxide semiconductor (HMOS) sensor works by heating a small substrate to high temperature (around 300-deg F / 149-deg C). At this temperature, the substrate is very sensitive to ozone and exhibits a change in resistance that is proportional to to the amount of ozone which contacts its surface. The circuitry of the monitor interprets this change in resistance and displays the corresponding ozone level on the display as either PPM or PPB.
Very responsive to low levels of ozone ozone (below 0.1 ppm)
Slower response time to ozone (compared to electrochemical)
Very sensitive to interference
Shorter battery life due to heated sensor element
Not linear at ozone levels above 1 ppm
Ceiling Temperature threshold of 122F or less (depending on model)
The Ozone molecule has an absorption maximum at 254 nm. A UV lamp emmiting 254 nm wavelength of light is used to measure the absoption of ozone within a chamber. This is measured via a photodiode with a built in interference filter centered on 254 nm wavelength
Very accurate (within 1%)
Very linear at any ozone levels
Low ppb detection limits with accuracy
Minimal cross sensitivity to other gasses or interferences
Can read high concentrations (20% or higher)
Durable design with excellent longevity
Bench mount (no handheld)
Ozone badges are one time use cards that use a color change indicator. The indicator used is a small paper strip or circle that is oxidized in the presence of ozone.
There are three primary technologies used to monitor and measure ozone: Electrochemical cells, HMOS / GSS, and UV. Today we will be giving a brief overview of UV ozone analyzers and their use.
UV-based ozone analyzers function on the principle that ozone particles will absorb UV light with a wavelength of 254 nm. When this wavelength of UV light is created and passed through an air chamber, the amount of UV light absorbed is proportional to the amount of ozone present in that airspace. The amount of UV light absorbed in the chamber is interpreted as ozone concentration and displayed or output for our use.
There are many advantages to this technology, but the primary ones are its accuracy and stability over a wide range of ozone concentrations. Depending on the design of the instrument, a UV ozone analyzer may be able to provide reliable, stable readings for single-digit ppb concentrations of ozone. Alternately, another UV analyzer may provide high concentration readings up to 20% by weight (many thousands of ppm).
Another benefit of UV Absorption is its resistance to interference by other gases. Since the principle used is very wavelength-specific, few other gases interfere. This results in much more accurate readings, even in outdoor environments.
The most noticeable downside of UV Absorption technology is price. It is more expensive than HMOS, GSS or electrochemical technologies. For many customers, however, the reliability of UV technology compared to the risk of false readings from other monitors makes UV technology well worth the cost.
Industrial ozone control
Ozone process off-gas measurement
Semiconductor fabrication facilites
Ozone compatibility testing
Here are a few monitors offered by Ozone Solutions that utilize UV Absorption technology:
There are three primary technologies used to monitor and measure ozone: Electrochemical cells, HMOS / GSS, and UV. Today we will be giving a brief overview of Electrochemical sensors and their use.
When ozone contacts an electrochemical cell, it causes electrons to flow. This electric current varies in proportion to the amount of ozone present, so the monitor can interpret this signal as ozone concentration and display or output those values for us.
Due to their construction, electrochemical ozone monitors have several properties that make them unique. One of these is long battery life. Due to the low power consumption of their sensors, they have the longest battery life of any ozone monitoring technology.
Another benefit they share is a resistance to interference from other gases. Electrochemical cells are each built with materials that are designed to be as specific to ozone as possible. While not as good as UV technology in this regard, there are certain situations where they are a necessity.
One downside that these sensors have in common, however, is their limited sensor life. Electrochemical cells will deplete over time even while in storage, so keeping a regular replacement schedule is advised.
Portable ozone safety monitoring
Ozone monitoring & control, especially if interfering gases are a concern
Here are a few monitors offered by Ozone Solutions that utilize Electrochemical Sensor technology:
There are three primary technologies used to monitor and measure ozone: Electrochemical cells, HMOS / GSS, and UV. Today we will be giving a brief overview of HMOS / GSS sensors and their use.
HMOS (Heated Metal-Oxide Semiconductor) and GSS (Gas-Sensitive Semiconductor) based ozone sensors function by heating a small semiconductor substrate to high temperatures, causing it to be extremely sensitive to ozone. This is seen as a change in the resistance of the material, which is measured by the circuitry, interpreted as ozone, and either displayed or output for our use.
One of the key benefits of this sensor technology is that it is very inexpensive, allowing widespread adoption at many facilities. It is commonly used for both portables and wall-mount ozone monitors.
Another advantage to semiconductor-based sensors is their solid ozone response below 0.1 ppm. This allows them to be used in many ambient ozone safety scenarios, with a display resolution as fine-grained as 1 ppb. While not as stable or sensitive as UV-based ozone analyzers in this range, they are worth consideration for ambient safety scenarios where low ozone concentrations are expected.
Disadvantages include a short battery life (due to the continuous heating of the sensor) and the extended warm-up time that the sensor requires.
Ambient ozone safety monitoring
Ozone control scenarios, especially at levels below 0.1 ppm
Here are a few monitors offered by Ozone Solutions that utilize HMOS Sensor technology:
One question we commonly receive is “Do your ozone monitor calibrations come with NIST traceable calibration certificates?” The answer is simply yes, our ozone monitor calibrations (and our ozone analyzer calibrations) do indeed come with NIST traceable calibration certificates.
Another question we receive somewhat less often is, “What IS a NIST traceable calibration?” We will discuss that topic briefly here.
To start out, NIST is the National Institute of Standards and Technology, which was founded in 1901 and is responsible for governing national standards of measure here in the United States (among other things). From the NIST website:
NIST is responsible for developing, maintaining and disseminating national standards - realizations of the SI – for the basic measurement quantities, and for many derived measurement quantities. NIST is also responsible for assessing the measurement uncertainties associated with the values assigned to these measurement standards. As such, the concept of measurement traceability is central to NIST’s mission.
Traceability, then, refers to your ability to follow documented calibration paperwork in an unbroken chain all the way back to the official NIST standard itself. The calibration certificate for any ozone monitor should list the source that it was calibrated against. If you obtain the calibration sheet for that source, you will again find the source that it was calibrated against and so on and so on. If you follow the chain, you will eventually find a calibration source that was calibrated at NIST itself.
Note that with each “hop” of the traceability chain there is some amount of uncertainty that is added to the resulting calibration. The more “hops” from NIST, the larger the uncertainty. The length of the traceability chain will give you an indication of how much uncertainty you may encounter as compared to the NIST standard.
What is the benefit of all this paperwork? One standard. The NIST ozone standard is deemed to provide the one, true standard for an ozone measurement. As consumers, if you purchase an ozone monitor that has a NIST traceable calibration certificate, you can rest assured that the measurements indicated by your ozone monitor should be comparable to a true ozone measurement.
When you purchase a piece of ozone detection equipment from Ozone Solutions, or when you have ozone monitors calibrated at Ozone Solutions, you will receive a NIST traceable calibration certificate which indicates our dedication to quality ozone detection products and quality service. Ozone Solutions prides itself in having a short NIST traceability chain, minimizing uncertainty to provide the most accurate ozone readings possible.
For further information on our calibration process, please refer to the following links:
Whether you are installing an ozone monitor for the first time or the 100th time, there is always one question that needs to be answered:
Where should I install my ozone sensor?
As you will see, the answer to this question depends on many variables – and is specific to your particular application. Nevertheless, we will tackle that topic here and give you enough information to install your ozone monitor confidently!
Unlike gas detection for some specific industries, OSHA does not specify the placement of ozone monitors or ozone sensors. Rather, OSHA specifies the PEL (Permissible Exposure Limit) for ozone at 0.1 ppm and leaves the rest up to you.
When deciding on ozone sensor placement, you should keep the following in mind:
Ozone is heavier than ambient air
Consider ventilation and airflow to determine where fugitive ozone may spread
Some monitors include remote sensors (wired)
Place ozone sensors near equipment / tubing where ozone leaks may occur
Place ozone sensors in areas that will be occupied by employees or visitors
Consider possible interferences in the area of the monitor
Each application is unique and will require its own consideration
Elaborating on this list:
1. Ozone is heavier than ambient air. This means that ozone will tend to pool first in low-lying areas such as crawl-spaces or along the floor. That said, most ozone monitors are placed at chest height. Placement at chest height means that the monitor is easily visible to most passers-by while monitoring the safety of air within our “breathing range”. If employees or contractors spend a lot of time under equipment or in crawlspaces, however, then alternative sensor placement needs to be considered.
2. Consider ventilation and airflow to determine where fugitive ozone may spread. If ozone is in use, or if your equipment is leaking ozone, that air will tend to drift with the airflow of your building. Consider fans, return-air vents, doors and windows to try and predict where air may flow. If you install an ozone sensor near your equipment but the airflow leads the opposite direction, then you will only detect ozone leaks late (if at all). Keep in mind that your airflow patterns may cause ozone to collect in “pockets” instead of dispersing and spreading. These stagnant areas should be kept in mind while formulating your ozone detection strategy as well.
3. Some monitors include remote sensors (wired). Some ozone monitors have their sensor positioned at the end of a cable, allowing you to mount the display in one location and the sensor in another. This allows you to mount the sensor in a machine room, for example, while have the monitor and alarm indicators outside. This capability is convenient for some, unnecessary for others – but it is a good point to keep in mind while choosing your equipment!
4. Place ozone sensors near equipment / tubing where ozone leaks may occur. This may seem obvious, but if your primary purpose is to detect ozone leaks then you will want to have the sensor located near the equipment and tubing in question. Your first line of defense to prevent high ozone levels in an office is to watch for ozone leaks in the adjoining machine room itself.
5. Place ozone sensors in areas that will be occupied by employees or visitors. This applies to all areas where ozone is in use, or where ozone may drift to (see point #2 above). Visitors or contractors may have little or no prior experience with ozone exposure safety, and even some of your everyday employees may be unable to detect ozone leaks by smell (a reminder that your sense of smell is never a reliable indicator of ozone concentration). Positions sensors and alarms to alert necessary persons of high ozone levels.
6. Consider possible interferences in the area of the monitor. For some ozone monitor technologies, placement of a sensor near chemical storage or areas of chemical use may result in interference with your ozone monitor. This effect is usually in the form of false positives, but certain chemicals can artificially depress the ozone readings detected by a sensor. If you are using an HMOS or GSS ozone monitor, for example, you should never install them in an area where they will be exposed to silicone fumes (the silicone will form a shell over the heated sensor junction, permanently preventing them from detecting ozone).
7. Each application is unique and will require its own consideration. Even if you have installed ozone monitors at multiple sites, each installation may have unique factors that affect sensor placement. Keep the above points in mind as you plan out your ozone monitoring strategies, browse our website for further details, and contact us with any remaining questions you have!
Ambient Ozone Monitors – The descriptions, images, videos and selections here will help inform you further regarding sensor placement.
In a cautionary tale to all companies that use ozone, a UK soft drink company (Cott Beverages from Leicestershire, UK) was recently fined for exposing an electrical contractor to unsafe ozone levels in July 2010.
The contractor in this case was performing work on unrelated equipment in a machine room that also housed ozone equipment. This ozone equipment had apparently developed a leak during March of 2010 and had not been adequately repaired, nor were proper steps taken to alert others to the danger.
The symptoms experienced by the contractor were consistent with those of an acute irritant asthma attack, said doctors involved with the situation.
Overall, the fine handed down by the Magistrate Court was equivalent to about $50,000 USD.
The moral of the story is that a lax attitude about ozone safety can result in harm, especially if somebody with pre-existing medical conditions (such as asthma or other respiratory disorders) is exposed to ozone. Sadly, this scenario is entirely preventable with proper ambient ozone safety monitoring, preventative maintenance and (generally inexpensive) repairs.
Refer to the following links for further information that can help your company avoid this same fate:
Oxygen is required to produce ozone. While oxygen is found in the air we breathe, the level of oxygen is low (~20%) and not ideal for ozone generation. Due to this, most ozone generators will use an oxygen concentrator to provide 90-95% pure oxygen. Ozone Solutions provides oxygen concentrators for this purpose.
If you are using an oxygen concentrator as part of your ozone system you may be wondering, is my oxygen level sufficient for ozone production? To help with this we have recently added handheld oxygen meters to our product line to answer that exact question.
Max-O2: Hand-held Oxygen Analyzers
Max-OM-25: Hand-held Oxygen Analyzers
Click on the images of either meter to be directed to the page on our website with more details for each device.
These meters are the same meters our service technicians hear at Ozone Solutions have been using for years. We have also offered oxygen meters for rent for our customers who may have a short term oxygen meter need.
Here at Ozone Solutions, we commonly receive phone calls and emails asking about ozone safety. Perhaps the most common of these questions is “What are the OSHA ozone safety limits?”
The simple answer to this question is the following: 0.1 ppm ozone (on average) during any 8 hour time period.
The 0.1 ppm value is what OSHA defines as their PEL (Permissible Exposure Limit), and most ozone monitor manufacturers have standardized on this value as the default for alarm indicators. Ozone monitors and detectors will often have either an audible or visual alarm that goes off when the ozone level reaches 0.1 ppm.
What does this mean for you?
If you need an ambient ozone monitor to ensure employee safety, you should consider buying a monitor with alarms (audible, visual, or both) that indicate 0.1 ppm of ozone. This will ensure that any ozone leaks or excess ozone exposure will be noticed and remedied, and ensure your working environment remains within OSHA compliance.
For further information about ozone safety in the workplace, refer to the following links and watch our video below!
This Ozone Journal is a blog managed by the employees of Ozone Solutions. The purpose of this blog is to inform and educate the readers about the world of Ozone, provide news about the ozone industry, and have an easy opportunity to inform about new ozone products.
Check back often, ask questions, and let us know if there is anything you would like to hear about.
What is ozone?
Ozone is an oxidant. Ozone (O3), sometimes called “activated oxygen", or "triatomic oxygen", contains three atoms of oxygen rather than the two atoms we normally breathe. Ozone is the second most powerful oxidant in the world and can be used to destroy bacteria, viruses, and odors.
Ozone is a gas at ambient temperatures and pressures with a strong odor. Ozone can be produced as a gas from oxygen in air, or concentrated oxygen. This ozone gas can be dissolved into water, or used in the gas phase for a variety of applications discussed in this Journal.