By Becca Dodds, Marketing Manager – Portable Gas Detection, Draeger Safety UK
From wastewater facilities and food processing plants to telecommunications sites and breweries, gas safety presents serious workplace risks in a wide range of industries.
Portable gas detectors have long been a crucial tool for alerting workers to the presence of asphyxiating, toxic or explosive gases, or when oxygen depletion occurs. However, the significant changes to working practices over recent years, as well as major advances in technology in this area of safety, highlight the importance of understanding the fundamentals of portable gas detection. In turn, having a solid grasp of the basic foundations of this important area of safety enables greater comprehension – and potential use – of some of the latest innovations in the field.
What is a portable gas detector?
Portable gas detectors, sometimes referred to as personal or compliance monitors, are compact, battery-powered devices. They are worn on the person, usually attached to clothing at chest height in the breathing zone. They provide early warnings of the presence of a range of toxic or flammable gases or vapours, or low oxygen levels, in the immediate surrounding area.
These devices support both single and multi-gas detection; the latter can monitor several gas hazards simultaneously using individual or dual gas sensors in one device. In wastewater treatment settings, for example, sensors may monitor for methane, hydrogen sulphide, carbon monoxide and oxygen deficiency to protect employees working in such environments.
When a portable gas monitoring device detects any gas that reaches preset levels, it will activate an alarm and start flashing/vibrating. The alarm is designed to be clearly heard and seen by the wearer, allowing them to take immediate action to protect themselves and others by evacuating the danger area.
Gas detection regulations in the UK
Gas detection is tightly regulated in the UK to ensure worker safety, and there are key regulations which employers need to adhere to keep their employees safe.
- EH40/2005details Workplace Exposure Limits (WELs) for a variety of hazardous substances, including gases. Adhering to these limits is crucial for maintaining a safe working environment, and employers have a duty to ensure that no employee is exposed to any concentration of substance more than the WELs for that substance.
The WEL values are split into two parameters: the Long-Term Exposure Limit (LTEL), which is the maximum exposure permitted over an 8-hour period (also known as TWA – Time Weighted Average) and the Short-Term Exposure Limit (STEL), which is the maximum exposure permitted over a 15-minute reference period.
Gas concentration is measured in a variety of units such as Vol% and PPM, (Parts Per Million) e.g. if a detector reads 50 PPM of carbon monoxide, this means 50 parts of carbon monoxide in every million parts of air.
Examples of common gases and their UK workplace LTEL exposure limits include:
Carbon Monoxide (CO): WEL of 20 PPM over an 8-hour time-weighted average (TWA)
Hydrogen Sulphide (H₂S): WEL of 5 PPM over an 8-hour TWA
An example of a common gas and its UK workplace STEL exposure limit would be:
Chlorine (Cl): WEL of 0.5 PPM over a 15-minute TWA
The LTEL is designed to protect the workforce from concentrations of contaminants, which over a sustained period could cause long-term chronic ill health effects. The STEL exposure limit relates to peak exposure incidents and is designed to protect against immediate acute ill-health effects.
- In additionto EH40, it is important to adhere to ISO 10156:2017, the international standard that provides a method for determining and calculating the flammability of gases and gas mixtures, including how to assess whether a mixture is flammable based on its composition and how inert gases reduce flammability.
Central to this is understanding the Lower Explosive Limit (LEL) and Upper Explosive Limit (UEL): the LEL is the minimum concentration of a gas in air below which ignition cannot occur, while the UEL is the maximum concentration above which there is insufficient oxygen for combustion. Gas detection systems are typically set to alert at low percentages of the LEL (often 10–20%) to provide early warning and allow intervention well before conditions become explosive, ensuring compliance with legislation and protecting people, plant, and property.
As an example, hydrogen sulphide (H₂S) presents a significant flammable as well as toxic risk in industrial and confined-space environments. It is a colourless gas with characteristic “rotten egg” odour at low concentrations, although reliance on smell is strongly advised against because olfactory fatigue occurs rapidly.
From a flammability perspective, H₂S has a wide explosive range in air, with a Lower Explosive Limit (LEL) of approximately 4.3% by volume and an Upper Explosive Limit (UEL) of about 46%, meaning it can ignite over a broad range of concentrations if an ignition source is present. This wide range increases the likelihood of forming an explosive atmosphere, particularly in poorly ventilated areas such as sewers, tanks, and process vessels. For health and safety professionals, it is critical to recognise that flammable conditions can co-exist with severe toxicity at much lower concentrations, so gas detection, effective ventilation, ignition source control, and alarm setpoints based on a percentage of the LEL are essential to managing both explosion and acute health risks associated with H₂S.
By adhering to both EH40 and ISO 10156 guidelines, employers can reduce the risk of gas exposure and flammability, protecting their teams from health issues, serious injury and, in the worst-case scenario, fatality.
Uses
Portable gas detectors are typically used for three key reasons:
- Personal safety – to protect workers fromimmediate or long-term exposure
- Operational integrity – toidentify leaks and prevent fires or explosions.
- Regulatory compliance – to meet occupational health and safety regulations.
Fixed and portable gas detection devices are often used in combination, but each has a different functionality, so it is crucial that the appropriate type of detector is used for the situation, activity and risk. While fixed gas detectors provide continuous area monitoring in high-risk zones, portable detectors offer personal protection and continuous monitoring for workers operating in the field or in confined spaces and during maintenance tasks, and when moving through areas where there is the potential for a leak. Combining both detection techniques ensures constant coverage, verification of fixed-system alarms, and on-the-go detection in areas where fixed systems aren’t practical, delivering comprehensive safety and regulatory compliance.
Effective safety procedures
Employers must have an effective safety procedure in place so that employees clearly understand what to do in the event of a gas leak.
To optimise gas safety in the workplace, there must first be a risk-assessment process that identifies potential gas hazards, establishes control measures and ensures all equipment is properly maintained and routinely inspected. In addition, an emergency procedure should be put in place, detailing what employees need to do in the case of the alarm sounding, with regular safety drills carried out.
Key elements of a gas safety procedure include:
Ongoing and effective employee training
Training plays a central role in an effective gas safety procedure within the workplace by giving employees the knowledge and practical skills they need to identify warning signs of gas leaks, understand detection systems, follow safe handling and storage procedures, operate equipment safely, and respond correctly in emergencies.
Responding quickly to an alarm is fundamental – employees should never ignore an alarm or assume it to be anything other than real. Regular drills should be carried out to ensure regular practice of the process to be followed in the event of a need for the evacuation of the area, whether a site, confined space or remote working area. As well as being clearly communicated to all employees, these drills should be regularly tested and within the evacuation process, it should be reinforced that no one should re-enter an area until it has been confirmed safe from lingering contaminants.
Furthermore, regular refresher sessions reinforce these skills and address any changes in technology, regulations, or workplace conditions. By building competence, confidence, and situational awareness, training helps create a proactive safety culture in which workers can prevent incidents, respond quickly to potential risks, and protect both themselves and their colleagues.
Regular maintenance
Regular maintenance of portable gas detectors is also an essential element of the safety procedure.
Portable gas detectors are there to save lives, so they must be regularly maintained in line with the manufacturer’s guidelines. This maintenance may typically include visual inspection and bump testing to confirm there is no damage and that the device’s sensors and alarms are responding to the target gases, and this is recommended to be carried out before every use.
Scheduled calibration
The calibration of gas detection devices is extremely important to ensure measurements are accurate, ensuring alarms will be activated at the correct exposure limits.
Sensors are used for continuous measurements and are likely to drift over time, so they need adjusting periodically. The calibration frequency will depend on the device type, sensor/gas type, application and local legislation. It is important to check the calibration periods with the manufacturer.
Conclusion
Portable gas detectors save lives every day — but only when used correctly and when an effective safety procedure is in place. Employers and employees using portable gas detection must understand the key terminology, regulations, and potential health impact of gas exposure to maintain a safe working environment: ensuring every worker goes home safe, at the end of every day.
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