Portable Gas Detection

Safety should always be of the highest priority—it is the reason these detectors were invented, after all.

This Q&A with Larry Medina, product portfolio marketing manager for portable gas detection devices in North America at Draeger, Inc., discusses key features and how to identify the “right” device for your own circumstances.

1. What is one of the most important characteristics safety managers should look for in a portable gas detector?
When it comes to portable gas detection, device adaptability is key. Since hazardous gases can present themselves in a myriad of environments—spanning industries such as oil and gas, wastewater treatment, pharma, and chemical and fire services—portable gas detectors need to be able to identify a variety of threats. By performing a Process Hazard Analysis (PHA), safety managers can identify and comprehend potential risks present at a given work site.1 Because each work site presents a unique set of challenges, companies can leverage the PHA to preemptively plan for and introduce necessary steps to mitigate risk and danger for on-site workers. Broadly speaking, PHAs will identify gas-based risks that fall into three categories—potential for explosion, oxygen enrichment or oxygen deficiency ,and toxic gas poisoning.

In work sites where there is a potential for explosion, such as mines, refineries, and chemical plants, flammable gases and vapors are typical ingredients for ignition. If the ratio of a flammable gas to oxygen (or air) lies within a certain Lower Explosion Limit (LEL), an ignitable mixture can form. The LEL of almost all known flammable gases and vapors lies roughly between 0.5 to 15 Vol.-%, however, it's crucial for safety managers to understand the specific potential hazardous materials that can arise on site and ensure that their suite of gas detection equipment can effectively alert workers in such an event.

The second category pertains to oxygen enrichment and oxygen deficiency. To begin with the former, the heightening of the atmospheric oxygen concentration can profoundly impact flammability and even cause materials to self-ignite. Oxygen deficiency, on the other hand, is often caused by the release of an inert gas. Typically, oxygen deficiency becomes hazardous in stages. If the air's oxygen concentration dips below 17 Vol.-%, workers may be in an early stage of danger. If the air's oxygen concentration drops even further—between 11 and 14 Vol.-%, for example—workers may experience unnoticeable decreases in physical and mental performance. If the oxygen concentration dives again—below 11 Vol.-%—workers can lose consciousness.2

Like oxygen deficiency, risk of poisoning via the toxic gases themselves can impact work sites that perform industrial processing. Notably, authorized commissions in several countries define the concentrations at which these gases are considered dangerous. In certain regions, gases are deemed "very toxic" if their LC50 is less than 0.5 g/m3. Fluorine, hydrogen cyanide, and sulfur tetrafluoride are examples of gases that can fall under this designation.3

Companies and safety manages that complete a PHA can determine what specific capabilities they need in a portable gas detector, and make the next step in identifying the "right" device.

2. Given the breadth of their capabilities, what are some "must-have" features of portable gas detectors?
There are several essential features that can be important to consider when selecting a portable gas detector. First, it can be important to assess a portable gas detector's durability. Sturdy, resilient detectors will likely last longer than their weaker counterparts—whether they are exposed to traditional wear and tear or to the harshest of environmental conditions. Detectors with shock-proof, chemical-resistant, and rubber-based coatings tend to have longer lifespans. The same can be said for detectors that meet the requirements of IP68 (an indication of high resistance to water and dust ingress).

Ease of use can be another important feature to consider when selecting a portable gas detector. During an emergency, a device that is simple to operate and read can help speed up the appropriate response. For example, a detector that features multi-toned audio signals, a vibrating top and bottom, and bright, flashing, 360-degree LED visual signals can help prevent missed alarm signals. If drilling or other loud procedures were to obscure the detector’s audio alarm, for instance, workers would still be alerted to potential danger via the detector’s visual and vibrating emissions. Language-free interfaces exemplify another easily understood and operable detector attribute. In the event of an emergency, this feature can help workers evaluate potential threats in a universally understandable manner.

Quick sensor response times also can benefit worker safety. Consider the following hypothetical scenario: Two workers are donning portable gas detectors in an area where hydrogen sulfide (H2S), a notoriously dangerous gas, is present in a high concentration. One worker’s device has a sensor with a t90 time of 15 seconds, and the other worker's device has a sensor with a t90 time of 30 seconds (the first worker's sensor can measure 90 percent of a test gas' concentration in 15 seconds; the second worker's sensor can measure 90 percent of a test gas' concentration in 30 seconds). Initially, neither detector alerts the workers to the hydrogen sulfide's presence. At the 15-second mark, the first worker's device reads 90 percent of the gas concentration value and emits an audible alarm. The second worker's device remains silent as it is reading about half of that amount, rendering him vulnerable to the effects of the gas. Shortly thereafter, the first worker's device emits its A2 alarm (main alarm), effectively notifying the worker that he or she needs to evacuate the area. By the time the second worker's device emits its A2 alarm, the second worker is likely already experiencing symptoms such as eye irritation, dizziness, nausea, headache, coughing fits and laborious breathing.

As this situation illustrates, quick sensor response times are extremely important. Without them, workers can suffer symptoms of gas exposure.

3. Aside from these features and understanding the three categories of danger, how can safety managers effectively distinguish the detector that will work best for their work site?
Safety managers can narrow down their list of potential candidates by evaluating the specific needs of their applications. For example, a work site may require a portable gas detector that's suitable for confined space entry, an application that presents unique hazards due to its lack of ventilation. In this scenario, the safety manager should consider selecting a device that is compatible with external pumps or has an internal pump, as well as the long probes or hoses used for confined space clearance measurements.

Of course, if the need is a detector to serve as a personal monitoring device once the clearance measurement has been completed, they also should consider the device’s size and weight. Opting for a smaller and lighter detector may be less likely to hinder workers’ range of motion when attached to the workers' clothing.

As with confined space entry, leak detection may warrant a specific type of detector. Leaks can occur anywhere gases and liquids are transported or contained. It is crucial to identify and assess leaks as quickly as possible so that the appropriate actions can be taken. Thus, detectors used for leak detection must have especially sensitive sensors that reliably detect minute fluctuations in gas concentration.

4. Once safety managers have selected their detector of choice, how do you recommend they ensure equipment efficacy?
Workers often depend on their portable gas detectors every single day, so it is essential to ensure that they are functioning properly. One way to check a portable gas detector’s accuracy is to perform a bump test. There is not a singular concrete way to execute such an assessment, but generally, the gas detector evaluator first needs to establish the type of results he or she is seeking. For example, is he looking for qualitative results that demonstrate that the device works as expected, or is he looking for quantitative measurements to assess device accuracy?

Then, the gas detector evaluator needs to decide whether he would like to initiate a quick bump test or an extended bump test. A quick bump test assesses whether the sensor will exceed the first alarm threshold. When performing this type of test, the evaluator may find it useful to note that the alarm might not go off unless the sensor stays above the limit for a certain amount of time. To ensure device sensitivity, the evaluator may want to consider selecting a test gas that is not too far above the first alarm threshold. An extended bump test differs from a quick bump test in that it constitutes a more comprehensive assessment. It normally serves to evaluate whether the sensor complies with a gas concentration within a given window.

Regardless of which test an evaluator chooses to perform, if a sensor is not functioning properly, its corresponding detector should not be used. Safety should always be of the highest priority—it is the reason these detectors were invented, after all.

References
1. https://www.osha.gov/SLTC/processsafetymanagement/hazards.html
2. https://www.draeger.com/Products/Content/sensors-ca-br-9046571-en.pdf
3. https://www.draeger.com/Products/Content/sensors-ca-br-9046571-en.pdf

This article originally appeared in the December 2017 issue of Occupational Health & Safety.

OH&S Digital Edition

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    December 2017

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