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Volatile organic Compounds


Carbon Dioxide


Volatile organic Compounds


Volatile organic Compounds




Indoor Air Quality (IAQ) is a critical aspect of building health and safety. The air we breathe can have a major impact on our health and wellbeing, especially if we spend a majority of our time indoors. Poor IAQ can cause respiratory problems, headaches, allergies, and other illnesses. At Critical-Environments, we provide customised solutions to monitor and record the air quality of any indoor environment.

Indoor Air Quality (IAQ)







What is Indoor Air Quality?

There are many published articles and studies done that confirm the ill-effects of poor air quality on human beings whether it is in our homes, workplace or outside in the public space. The effects of poor air quality on us is outside the scope of this web site but there are a number of links available to published documents and other websites that deal with this in more detail.

Having been involved in Building Management Systems (BMS) for the past 28 years I will attempt to explain the cause of poor air quality, how it can be monitored and most of all how it can be controlled. The 'Code of practice of air quality control' recently issued by the Irish Health & Safety Authority has prompted employers to look at the air quality in their place of work and conduct the necessary inspections according to the 'Code of Practice'. It is also worth mentioning that whilst temperature and humidity of our ambient air is very important, they are looked on more for comfort rather than a potential to cause long term harm to an individual. The pollutants discussed in the following sections are ones that can be ingested into our bodies and potentially have short or long term harmful effects.

Poor Air Quality Components

Whilst there are quite a number of toxic components potentially in our air, there are only a select number of them that we need to be concerned with on a day-to-day basis. This would apply to the ambient air in our homes and in our place of work.

The air quality components that will be discussed are the variants of Particulate Matter (PM), Volatile Organic Compounds (VOC) and our well known air pollutant, Carbon Dioxide (CO2).

The sections below will explain what each pollutant is, where it comes from, how it can be measured and most importantly, how can we prevent it from entering and lingering in our homes and work places.

Carbon Dioxide (Co2)


Scientific Representation of Co2

CO2 is an invisible, colourless and odourless element of the air that we breath in on a daily basis. The concentration of CO2 varies considerably and there are numerous factors that can effect it. The ambient outdoor air has an average level of 400ppm but more current studies have indicated a slightly higher average than this.

So what is ppm? and at what level does it become harmful to us?

PPM stands for 'Parts per Million', this means that for every million parts of air there are 400 parts of CO2.

Indoor air in occupied spaces is generally higher than this unless there is significant ventilation whether by mechanical means or just having windows and doors open to allow increased air changes in the space. CO2 levels up to 1000ppm are considered unharmful, above this level up to 1500ppm is considered to be above average and the occupants should consider opening doors and windows or switch on mechanical ventilation if installed. Above 1500ppm is potentially harmful and can lead to fatigue, dizziness and other similar symptoms. 

Monitoring Co2

Following the Coronavirus pandemic, the market is now flooded with hundreds of type and models of CO2 sensors. Many of the sensors come with an LED display showing the CO2 level and also temperature & humidity. We at Critical-Environments have tested many different models of Co2 sensors and have found significant differences between them.

There are 4 types of Co2 transducer used in Co2 sensors available on the market:

Non-dispersive infra red transducers are the most common on the market and is the type recommended by many state bodies for the measurement of Co2 in indoor spaces. Theses sensors are slightly more expensive than other types but are more accurate and have a faster response on measurements compared to other types of sensor.

There are different manufacturers of NDIR sensors and through our in-house testing we have found that the 'Sunrise' transducer out-performed all others we tested. The Sunrise transducer can be found on Tektelic, Sontay and Nexelec Sensors.

Transducer Types

  • Non-dispersive infrared 

  • Electrochemical 

  • Semiconductor

  • Catalytic combustion

Click link here to go to our Sensor Page

Reducing Co2 Levels in indoor spaces

Before you take any measure to reduce the Co2 levels in your indoor space you need to measure the CO2 levels over a period of time (typically 7-14 days) and analyse this data. There are many factors that will affect the Co2 levels such as occupancy, the use / non-use of mechanical ventilation, the ability to open windows and doors and the presence of indoor plants.

The Health & safety Authority 'Code of Practice for Indoor Air Quality' provides a practical Risk Assessment approach to help employers make a reasonable determination of IAQ in their workplace.

Once the assessment has been carried out it is important to install a Co2 monitoring system to create an awareness among employees and that they can see at any point what the Co2 levels are in their work space and consequently take action like opening windows etc.. .

Critical-Environments provide many options to visualise Co2 data whether it be on the sensor itself, local touchscreen display, the on-site Building Management System or on a cloud service.

Navigate to our webpage with all Visualisation Options or Please Contact Us

Particulate Matter (PM)

Particulate matter consists of very small particles which can be solids or aerosols composed of small droplets of liquid, dry solid fragments, and solid cores with liquid coatings.. Some of these particles occur naturally, and many are man-made. Particulate matter is usually referred to as PM with a number after it indicating the size of the particle. The two types of PM that are normally monitored are PM2.5 and PM10.These are the recommended particle size that should be monitored according to the CAFE (Cleaner Air for Europe) Directive and the WHO guidelines

PM10 means that the particulate matter is 10 microns or less in diameter, small enough so you could lay 10 of these particles across the width of an average human hair. PM2.5 signifies that it is particulate matter of 2.5 microns or less in diameter – you could lay 40 of these particles across the width of an average human hair.

Average Size Human Hair

Particulate Matter
Particulate Matter
Particulate Matter
Particulate Matter
Particulate Matter
Particulate Matter
Particulate Matter


Can penetrate
the lungs


Small enough
to be 

Where do these Particles come from?

The primary source of Particulate Matter is from solid fuel stoves where the burning of wood or coal emits significant pollutants into the air. The other primary source is in the form of Nitrogen Oxide and Nitrogen Dioxide and is emitted from diesel and petrol engines.

There are other sources of PM such as the dust generated from braking discs in cars and trucks which can be very harmful in high concentrations.

Measuring PM Concentrations

It is only very recent that technology has evolved and reduced the size of sensor to allow the measuring of particulate matter in commercial environments. The sensors use varying advanced techniques such as gravimetric and optical methods. PM is normally measured in Micrograms per cubic centimeter µg/cm3

The sensors available on the commercial market for use in office environments etc.. are not as accurate as those used in cleanrooms but are fit for purpose.See Nexelex sensor 'Sense'.

The CAFE and WHO guidelines indicate an upper threshold of 40 µg/cm3

Eliminating / Reducing PM Levels

Solid fuel burning in the place of work is most unlikely but the risk of polluted air coming in from outside can be quite high. Ultimately, the place of work needs to have close to zero PM concentrations Admittedly there are many examples where PM concentrations are high such as garages, manufacturing plants and other heavy industry.

There are different types of work environments, some more hazardous than others but consideration should be given to the following checks to be carried out (Indicative only)

  1. Is the incoming air filtered?

  2. If the air is already filtered in the mechanical ventilation, are the filters the correct specification?

  3. Is there an extract ventilation system installed, if so, does it extract sufficient air volumes?

  4. Do employees park their cars directly outside the office? (The exhaust fumes can enter the building through adjacent windows).

  5. If the central heating system is oil-fired boilers, is it located a safe distance from the offices and compliant with the building regulations?

Please refer to an extract from the HSA's Code of Practice to IAQ Risk Assessment

Volatile Organic Compounds (VOC)

Volatile organic compounds (VOCs) are organic chemicals that are  emitted as gases from certain solids or liquids. VOCs include a variety of chemicals, some of which may have short- and long-term adverse health effects. Concentrations of many VOCs are consistently higher indoors (up to ten times higher) than outdoors. Long-term exposure to VOCs can be harmful and should be minimised or completely eliminated in the work place.

VOCs are measured in Micrograms per cubic centimeter µg/cm3 or ppm

Where do VOCs come from?

VOCs are emitted by many man-made products such as those listed below:

Sources of VOCs

  • Paints and paint strippers

  • Air Fresheners

  • Pesticides

  • Refrigerants

  • Building Materials

  • Carpets & floor coverings

  • Wood lacquers and varnish

  • Solvents & Glues

  • Photocopiers & printers

  • Permanent markers

It should be noted that a new building or a new refit of an office are will potentially have much higher levels of VOCs than an older office.

There is a European directive on the amount of VOCs that you can have in your paint and must be appropriately marked on the outside of the container.

In general, low- or zero-VOC paints tend to be water-based and have significantly lower odor than oil/solvent-based paints. Flat (or matte) paints with fewer than 50 grams of VOCs per liter are generally considered to be low-VOC, while a zero-VOC paint is one with fewer than 5 grams per liter. Non-flat paints (such as satin and semi-gloss) are considered low-VOC if they have fewer than 100 grams of VOCs per liter. 

Volatile Organic Compounds
Types of VOCs

Measuring VOCs

Most smart IoT sensors on the market would have questionable accuracy (+/- 100 µg/cm3) otherwise you are looking at laboratory level instruments which would not be a practical solution.

The World Health Organization WHO recommends a guideline value of 0.3 mg/m³ (milligrams per cubic meter) for total VOCs in indoor air.

Critical-Environments offer the Nexelex Sense model which is a multi-function sensor and includes the measuring of VOCs.

A variant of this model also measures formaldehyde.

Eliminating / Reducing VOC Levels

As with other indoor air quality components, the key is ventilation of the space whether it is mechanical ventilation or natural ventilations suchs as windows and vents etc.. .

Filtration of incoming air is also very important as well as sufficient extract systems to remove contaminated air.

If a work place is undergoing a refit or decorating, measures should be put in place to check the credential of the paints and materials used to ensure compliance with the European directive on VOC content in solutions and materials.

Please refer to an extract from the HSA's Code of Practice to IAQ Risk Assessment

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