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TRANSDUCERS, TRANSMITTERS & SENSORS PROTECTING STAFF FROM HARMFUL VOCS
The cost of designing ION’s VOC and particulate sensors into OEM instruments, processes and systems is negligible in comparison with the potential costs and risks incurred by not specifying the best available technology
ION Science outlines the role of PID sensors in VOC detectors, which help keep workers safe
mployers have a duty of care to protect the health, safety and welfare of employees, so it is vitally important to keep workers’ occupational exposure to harmful gases within permissible limits. For businesses that handle hazardous vapours, failure to comply with this duty can have disastrous consequences, so trustworthy sensing technology is required. VOCs exist widely in almost every industry as key components of fuels, petrochemicals, paints, adhesives, cleaners etc. Most VOCs are flammable and potentially explosive, and are harmful to both health and the environment. Some are harmful to the skin or eyes, and can be absorbed, but their volatility means that VOCs can be inhaled, and may cause a wide variety of negative health effects ranging from minor irritation to cancer, and even death. Generally speaking, high concentrations (%levels) are necessary for combustion or explosion risk; low concentrations (ppm) can represent a toxic risk from short-term exposure, and trace levels (ppb) can cause long-term toxic effects.
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Organisations which fail in their duty to protect employees also risk huge financial losses from prosecutions, fines, and critical damage to their brands. Investments in health and safety monitoring and personal protective equipment, such as reliable gas detectors, are therefore
negligible in comparison with the consequences of failure.
Workplace risk assessments should identify the presence of potential VOC sources and enable the implementation of appropriate measures to mitigate the risks. Personal, wearable VOC detectors help protect staff that have been identified as being at risk, and routine inspections with portable VOC detectors help to identify fugitive emissions from leaks or spills from equipment, tanks, pipes, seals, valves, etc. In addition, fixed VOC monitors continuously monitor workspaces to check that levels do not approach or exceed exposure limits; raising alarms if they do. The minimum concentration of a combustible VOC necessary to support its combustion in air is defined as the Lower Explosive Limit (LEL). Importantly, toxic VOCs concentrations are orders of magnitude lower than explosive limits, so detection equipment should offer a range with sufficient sensitivity to measure trace toxic gases.
The health effects of exposure to VOCs depend on the concentration, the length of exposure, and the VOCs present. Workplace exposure limits (WEL) therefore exist for each VOC with short-term exposure limits (STEL) typically applying to the maximum concentration over a 15-minute period, and
time-weighted average levels (TWA) typically calculated over an 8-hour period. Gas detection equipment manufacturers have three main options for the measurement of VOCs. These are (1) electrochemical (EC) sensors, (2) metal oxide semiconductor (MOS) sensors and (3) photoionisation detection (PID) sensors. EC sensors are low-cost, but they only respond to VOCs that are electroactive; they require electronic optimisation for target VOCs, have a slow response time (minutes) and are cross-sensitive to other gases commonly found in the workplace. MOS sensors are also low-cost but suffer from baseline drift and humidity sensitivity. PIDs are the most in-demand and appropriate sensors for the measurement of VOCs for health and safety applications. This is because of their fast response (1-3 secs), and because they are the most selective technique to VOCs. In addition, with a choice of PID lamps it is possible to optimise the sensor for different applications, and known response factors enable quantitative analysis of specific VOCs.
Sensitivity to contamination and humidity is a major challenge, but these issues have been resolved within ION’s MiniPID sensor range. All MiniPID sensors have a patented design with a third electrode that nullifies potential humidity interference, delivering a stable signal from 0 – 99% RH.
The sensitivity of PID sensors is important in many applications; particularly where the sensors are deployed in the measurement of trace VOCs. Recognising the importance of this feature, ION’s MiniPID range includes the most sensitive PID in the world. Reliability is a critically important feature of such sensors, and ION’s MiniPIDs incorporate an ASIC chip, which continuously monitors lamp and sensor performance, providing fail-safe assurance of performance.
Dust and other forms of airborne particulates represent significant risks in the workplace; both as a combustion source and a breathing hazard. This means the requirement for monitoring equipment is growing alongside tightening regulations. Responding to this growing demand, ION has added the NextPM sensor to its portfolio. Thanks to its patented airflow control technology, Next-PM ensures years of maintenance-free measurements, even in highly polluted environments.
ION Science
www.ionscience.com
JUNE 2023 | PROCESS & CONTROL 33
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