It’s A Gas
By Jeff Cottrill
By Jeff Cottrill
There are many jobs in which workers risk inhaling dangerous gases or impurities. This is particularly true of work in confined spaces. Gas-detection or instrumentation devices that test the air quality of workspaces prevent workers from being canaries in a coal mine.
The scope of occupations that use some kind of instrumentation device is broader than one might think, according to Bob Henderson, president of Good for Gas Instrumentation (GfG), an international manufacturer of gas-detection products based in Ann Arbor, Michigan.
“It is an extremely large and horizontal group,” Henderson says, citing those who work in traditional oil and gas, the petrochemical industry, municipalities, heavy-industry power generation, mining, fire services, hazmat, emergency response and military programs. “It is just hard to find almost any category of employed individual who does not have the opportunity occasionally to need or use gas detection.”
Gas hazards are not limited to confined spaces, he stresses. Firefighters and other first responders may attend fuel spills, traffic accidents, train derailments and other outdoor accidents that can release hazardous gases or vapours, while hazmat workers are constantly under risk even when working in open spaces.
“At a refinery, every person onsite generally is going to have a gas detector or multiple gas detectors, because anywhere onsite is subject to certain hazards,” Henderson adds.
Although gas-detection devices come in different forms — most commonly, portable or wearable — they work on the same basic principle. A device contains at least one sensor designed to react to a specific type of gas. A single-sensor monitor can detect one gas, while others are built with multiple sensors for environments where multiple gas hazards can be present.
Dräger Safety Canada Ltd in Mississauga, Ontario carries a wide range of gas monitors. National accounts manager Manish Gupta says that its customers usually ask for detectors that identify one or more of four basic types of gases: lower explosive limit (LEL) gases, oxygen (O), carbon monoxide (CO) and hydrogen sulfide (H2S). “Generally, most gas monitors comprise those four sensors,” Gupta says.
Workers tend to carry these basic monitors in their shirt pockets or hook them onto their belts, so that they remain handy and can be readily deployed. In some cases, detectors can be custom-built for certain gases.
“One of the trademarks of our product line in particular is that we are very flexible on the type of sensors that we can put into an instrument,” says Dave Wagner, director of applications engineering and product knowledge with Industrial Scientific Corporation in Pittsburgh. The company manufactures portable single-gas and multi-gas instruments for a range of applications. Although basic four-gas instruments make up the depth of the company’s line, many variations are available.
“We can vary those sensors quite a bit and put in a sensor for sulphur dioxide, or we can put in a sensor for maybe chlorine or nitrogen dioxide, hydrogen cyanide, a variety of other gases, or we can put in some other more specialty sensors,” Wagner explains. An employer can even request infrared sensors, which can detect more specific types of combustible gases or carbon dioxide, he adds.
Another company that offers infrared gas sensors is Gas Clip Technologies, headquartered in Cedar Hill, Texas. According to service manager Jeremy Majors, the company carries monitors with infrared LEL sensors that run for as long as 60 days. “That is 60 days continuous, without having to be recharged,” he stresses, as opposed to competitor products that have to be recharged roughly after 12 to 18 hours.
The advantage of using a monitor that runs longer is that it can last for an entire shift. An employee who has to work a 24-hour shift will require two monitors just to get through one shift, Majors cites by way of example.
Instruments that are equipped with photo-ionization detectors have also become more common in recent years, Henderson observes. “And you see increasing numbers of substance-specific electrochemical toxic sensors and a few broad-range toxic sensors that are also available for use in multi-sensor and single-sensor instruments.”
Before an employer decides what type of gas monitors to purchase, it is necessary to conduct a risk assessment of the work environment to determine the atmospheric hazards to which workers may be exposed at any given time.
The next step is to determine what types of devices detect these hazards, and that can vary depending on the job or industry. In most confined spaces, the four basic gases (LEL, O, CO and H2S) are the minimal concerns, but many might also present the risk of volatile organic chemicals and other contaminants, which would require a device outfitted with extra sensors, Henderson explains. “If diesel exhaust is around, then you probably have nitrogen oxides to consider,” he notes.
In addition, hydrogen, ozone and ammonia tend to be major issues at many power-generating stations, depending on what kind of power the plant is producing. “In many cases,” Henderson adds, “the easiest way to deal with a specific hazard is by means of a substance-specific electrochemical sensor, because they don’t take much power, they are compact and they lend themselves to a small, easily used instrument.”
According to Majors, ease of use is important, and that can mean different things — from durability and portability to simplicity of operation. With a simpler product, “the employer can have his employees out doing their job, instead of worrying about their gas monitor,” Majors says.
READY TO USE
In Canada, the CSA Group standard C22.2 No. 152-M1984 (R2011), or Combustible Gas Detection Instruments, provides recommended practices for construction, performance and testing of gas monitors. To keep a detection device in working condition after purchase, CSA recommends that the worker perform a “bump check” before each use.
A bump test exposes each sensor of a gas-detection device to a specific, limited concentration of the appropriate gas. If the device’s reading is within an acceptable range from the actual amount of gas provided, the sensor is in good working condition. Some employers find it wise to do due diligence by having employees keep records of their bump tests.
Technological advances have made performing bump checks an easy process in recent years. “You now have bump-test stations, where you literally just put the device in the bump-test station and it does everything for you,” Gupta explains. “You don’t have to press any buttons, you don’t have to check any settings.” The station gives the user an “OK” indication to show that the device has passed the check.
Even after a successful bump check, workers must remain cautious when entering some confined spaces where certain pre-testing procedures may be required. “Before you lift the manhole cover,” Gupta cites by way of example, “pop open the cover a little bit, test the gas under the cover and then go in, because you don’t want a cloud of the contaminants sitting under the cover, and as soon as you open it, you suddenly inhale a cloud of gas.”
It is also vital to be aware of how suddenly the atmosphere can change. “As you work, you are changing how the air flows and the gas flows within that area, and so it can change from safe to unsafe very quickly,” Gupta adds.
In addition to bump tests, gas monitors must also undergo regular calibration to ensure accurate operation. Industrial Scientific Corporation advises its customers to calibrate their gas-detection devices monthly, as opposed to many manufacturers who recommend semi-annual or quarterly calibration.
Majors recommends doing a bump test after each time a monitor has been dropped or knocked around, to verify that the sensors are still operating properly. Keeping the sensors clean and clear is also important. “You want to make sure it is not caked with mud, dirt, sand, grit, those types of things,” he advises. “If they are dirty, then you’d want to replace the sensor filters themselves.
The shelf lives of sensors vary, and although they can be replaced easily once damaged, there may come a point when it is more feasible and cost-effective to replace the entire gas monitor, Majors advises. “The cost of replacing sensors may not warrant replacing the sensor. It may warrant purchasing a new monitor with a full warranty on it,” he says.
UP AND COMING
Honeywell Safety Products covers a large share of the gasdetection market in Canada, from basic single-gas and fourgas monitors to more complex products. One recent development that has become more prominent in gas detection and instrumentation is wireless technology, according to Calgary-based William Ball, Honeywell’s senior product specialist for portable gas detection.
“You have to have an attendant present who is keeping his eye on what is going on in a confined space while people are occupying it,” Ball says. Today, an attendant can stand outside of the confined space and use a wireless device that can pick up information from all of the gas detectors worn by the people in the space. In the past, an attendant had to conduct a pre-examination of the atmosphere in the space, determine whether it was safe and maintain verbal contact with the workers in the space while standing outside.
It is worth noting that the more complex and technologically advanced a gas detector is, the more expensive it is likely to be. Ball estimates that a simple four-gas or single-sensor detection device could cost an employer about $500, but additional features and powers will jack up the price, sometimes to as high as $2,500. Among product functions that can add cost are additional sensors, wireless capability and built-in radios. “Some detectors even have GPS capability as well,” Ball notes.
Regardless of price, Majors believes that technical advances in gas detectors will continue to develop and make the instruments more user-friendly. “With the technology we have today, we are able to do more, and I think people just expect that in every aspect of their life,” he says. “I think that they want their gas monitors to be able to be easier to maintain, easier to use and run longer.”
Jeff Cottrill is the former editorial assistant of OHS Canada.