Page 12 - Occupational Health & Safety, December 2017

GAS DETECTION
would still be alerted to potential dan- ger via the detector’s visual and vibrat- ing emissions. Language-free interfaces exemplify another easily understood and operable detector attribute. In the event of an emergency, this feature can help work- ers evaluate potential threats in a univer- sally understandable manner.
Quick sensor response times also can benefit worker safety. Consider the follow- ing hypothetical scenario: Two workers are donning portable gas detectors in an area where hydrogen sulfide (H2S), a noto- riously 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 work- ers to the hydrogen sulfide’s presence. At the 15-second mark, the first worker’s de- vice reads 90 percent of the gas concentra-
tion value and emits an audible alarm. The second worker’s device remains silent as it is reading about half of that amount, ren- dering 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 dizziness, coughing fits, and laborious breathing. As this situation illustrates, quick sensor response times are extremely important. Without them, workers can suffer symp- toms of gas exposure.
3. Aside from these features and under- standing the three categories of danger, how can safety managers effectively dis- tinguish 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 for confined space entry, an application that presents unique hazards due to its lack of ventilation. In this sce- nario, 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 com- pleted, they also should consider the de- vice’s size and weight. Opting for a smaller and lighter detector may be less likely to hinder workers’ range of motion when at- tached to the workers’ clothing.
As with confined space entry, leak de- tection may warrant a specific type of de- tector. 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 sen- sitive sensors that reliably detect minute fluctuations in gas concentration.
4. Once safety managers have selected their detector of choice, how do you rec- ommend they ensure equipment efficacy?
Workers often depend on their portable gas detectors every single day, so it is es- sential to ensure that they are functioning properly. One way to check a portable gas detector’s accuracy is to perform a bump test, so he must decide whether to initiate a quick bump test or an extended bump test. An extended bump test is more com- prehensive and normally serves to evalu- ate 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 func- tioning properly, its corresponding detector should not be used. Safety should always be of the highest priority—it is why these de- tectors were invented, after all.
REFERENCES
1. https://www.osha.gov/SLTC/processsafety- management/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
www.ohsonline.com
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