An Introduction to PIDs and VOC Monitoring

Volatile organic compounds (VOCs) are a wide range of natural and man-made chemicals. They are described as volatile because they have a low boiling point and evaporate readily at normal room temperature, releasing molecules into the atmosphere. They are potentially dangerous to health and the environment and can be found in a broad range of industries and locations.

Here, we identify different examples of VOCs, the personal and environmental impacts of over-exposure, as well as explore VOC monitoring solutions using photoionisation technology.

 

What are VOCs?

VOCs can be found at home, in the workplace or outdoors. They are extremely useful as they form the building blocks of many synthetic materials such as plastics, rubbers, glues and paints. They also play a key part in pharmaceutical manufacturing and fuel for transport and heating.

Toxic compounds that form VOCs can be found in industrial sources such as fuel vapours, solvents, spray booth paints, soil sample screening, chemical process control, heat transfer fluids, clean labs, and many more. VOCs can also be found in chemical spills and other environmental clean-up operations, and even in arson investigation, helping investigators with the cause of the fire.

Sources of VOCs in the home can include aerosol sprays, wood preservatives, paints, air fresheners, scented candles, nail varnish, dry-cleaned clothing, detergents, and wood-burning stoves.

How harmful are VOCs?

All VOCs have the potential to cause harm in high quantities over long enough periods, but the toxicity of each compound differs greatly. VOCs also have the potential to become an explosive risk, so monitoring levels is vital.

VOCs are also widely regarded as an air pollutant. When VOCs are released from industrial processes and vehicles into the atmosphere, they can contribute to poor air quality. Not only is this harmful to the environment but can also cause or aggravate health problems such as asthma, emphysema and other respiratory issues.

What is an acceptable VOC level?

VOC exposure guidance in the UK is covered by the HSE’s EH40 document, which lists workplace exposure limits. These Workplace Exposure Levels (WELs) are concentrations of hazardous substances in the air, averaged over a specified period of time and referred to as a time-weighted average (TWA). Two time periods are generally used: Long-term (8 hours); and short-term exposure limits (STEL) which is 15 minutes.

All mixtures containing VOCs should be supplied with a Material Safety Data Sheet (MSDS) which will specify the quantity of each VOC in the mixture, along with any actions that should be taken if exposure occurs.

In the UK, there are currently no indoor air quality guidelines for individual VOCs. In their absence, the Department for Education Guidance BB101: Ventilation, thermal comfort and indoor air quality (DfE, 2018) recommends the use of the WHO (2010) Indoor Air Quality (IAQ) guidelines.

What is a photoionisation detector (PID)?

A PID (photoionisation detector) can detect and measure VOCs and other gases from parts per million (ppm) to parts per billion (ppb), including:

 

• Aromatics, like benzene, toluene, xylene, pyridine, phenol, aniline, naphthalene (pesticide) 

• Olefins, like butadiene, cyclohexene, trichloroethylene, vinyl chloride, turpentine, limonene (cleaner)

• Bromides & Iodides, like methyl bromide (fumigant), n-bromopropane (degreaser), iodine (disinfectant)

• Sulfides & Mercaptans, like methyl mercaptan (natural gas odorant)

• Organic Amines, like methylamine, trimethylamine

• Ketones, like acetone, methyl ethyl ketone (MEK), methyl isobutyl ketone (MIBK)

• Ethers, like ethyl ether (solvent), methyl-t-butyl ether (gasoline additive), ethyl cellosolve

• Esters & Acrylates, like ethyl acetate (solvent), methyl methacrylate (glues), PGMEA

• Aldehydes, like glutaraldehyde (sterilant), acetaldehyde, formaldehyde (pressed-wood products)

• Alcohols, like butanol (solvent and fuel), isopropanol, ethanol, propylene glycol

• Alkanes, like hexane & isopar (solvents), octane & diesel fuels

• Some Inorganics, like ammonia, hydrogen sulfide, and phosphine (fumigant).

 

In addition, there is a response to chlorinated compounds, organic acids, silicate-, borate-, & phosphate-esters, isocyanates and many others.

Fuels like automotive petrol, diesel, kerosene and jet fuels are mixtures of aromatics, olefins and alkanes and give a strong response of VOCs.

A PID gives a continuous reading and will alarm when concentrations exceed set user-defined points. An internal pump is used to draw air sample in from distances up to about 30m (when using a sample tube).

PIDs are commonly used for industrial hygiene measurements to ensure that workers are not overexposed to toxic compounds in numerous sectors such as: Oil and Gas, Pharmaceutical and Medical, Food and Beverage, Government and Defence, Manufacturing, Semiconductor Manufacturing, Construction and Remediation, Aerospace, Water, Power Generation, Laboratories and Research.

VOC monitoring solutions from Shawcity

Shawcity provides a wide range of PID solutions for all fixed, portable and personal VOC monitoring. With instrument options available to hire or buy, Shawcity is dedicated to finding the best solution for your monitoring requirements.

For further technical information about PIDs and VOC monitoring visit: https://www.shawcity.co.uk/knowledge-hub.

 


 

 

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