When the smoke cleared following an explosion and fire at a crude oil refinery in Regina in early October, 36 workers had suffered injuries ranging from burns and smoke inhalation to minor bruises, sprains and abrasions. Thirteen employees required hospitalization.
The incident at the facility — operated by Consumers’ Co-operative Refineries Limited — involved the burning of some 1,800 kilograms of hydrogen and 36,000 litres of diesel, said Vic Huard, vice-president of corporate affairs for Federated Co-operatives Limited, which owns the company.
The accident illustrates the importance of proper monitoring for gases, whether they are combustible or toxic, an occasional hazard or a constant risk. “The gases you have present and the hazards will dictate what sort of gas detection you need,” says Manish Gupta, market manager with Draeger Safety Canada Ltd. in Mississauga, Ontario.
The choice of gas monitor boils down to two major types: fixed (stationary) and portable. Most instruments feature audible, visual and vibration alarms and two settings: a first warning alarm and a second “latching alarm,” which locks in place and cannot be reset until the hazardous gas levels have dissipated, Gupta explains.
When choosing a monitor, industry experts recommend taking a variety of factors into consideration, such as whether the gas is toxic or combustible, always present or part of a temporary spill scenario, in a confined space or for a general monitoring application, and the workplace activities or processes involved. “People forget gases are produced as part of the manufacturing process as well as a by-product of it,” says Don Galman, public relations manager for Honeywell Analytics in Lincolnshire, Illinois.
For their part, fixed detectors are generally more robust, heavily constructed and mounted in work areas where a process generates a known gas threat, Galman says. This type also includes standalone products, which offer the detector’s sensors, relays and display “all in one kind of box,” adds Greg Reeves, president of Arjay Engineering Ltd. in Oakville, Ontario. “You stick it on the wall, it does everything by itself.”
Fixed monitors that are not standalone typically use a remote sensor to send a signal to a control panel, meaning that one part cannot work without the other, Reeves explains.
Of course, fixed monitors can be used in conjunction with portable ones, Galman says. “When a gas is detected in an industrial environment by a fixed piece of equipment, you might use a portable to determine the more precise location of the leak,” he points out.
Compared with stationary devices, portable monitors offer considerably more choices. The most common type of portable monitor measures four gases: hydrogen sulphide (H2S), carbon monoxide (CO), oxygen and combustible gases (such as methane).
Reeves says the standard four-gas monitor would be used for sewer-entry confined spaces, where H2S, methane gas and oxygen deficiency are known hazards. In these environments, there are also usually trucks or cars nearby or workers using generators that may emit CO, he adds.
Industrial Scientific Corporation in Oakdale, Pennsylvania offers a lightweight, highly configurable instrument that can detect these four gases, ideal for confined space monitoring or continuous personal monitoring in potentially hazardous environments, notes a product sheet from the company. The detector uses a pump to draw samples from as far as 30 metres away and alerts users in dangerous conditions through an audible alarm, ultra-bright LED visual alarm and powerful vibrating alarm.
CHANGE OF SCENERY
In other workplaces, a different monitor may fit the bill. Options include photoionization detectors for volatile organic compounds such as glues, solvents or dry-cleaning fluids like percoethylene; electrochemical sensors for toxic gases like chlorine or ammonia; and catalytic bead or infrared sensors for combustible gases like butane or benzene.
“#34;The most popular sensors are catalytic for combustible gases, because they are low-cost, long-living and broad-range,” Reeves says. “They pick up anything.”
But there are some gases these sensors do not detect properly. The “downfall” of the catalytic bead sensor, which is used to monitor the lower explosive limit (LEL) of combustible gases, is that it is susceptible to poisoning by silicone and other gases, suggests Dave Wagner, director of product knowledge at Industrial Scientific.
As the sensor burns hot, the heat causes the silicones — if there are any in the air — to become gooey and stick on the sensor, Reeves adds.
“If you have silicone-containing vapour, it is oxidized or burned on the bead and what it leaves behind is a residue of glass,” explains Bob Henderson, president of GfG Instrumentation in Ann Arbor, Michigan.
“So you actually get silicone dioxide, a layer of glass that builds up on the active sites in the bead,” Henderson says.When molecules that a worker wants to detect enter the sensor, “they just bounce off the layer of impermeable glass.”
Additionally, a standard catalytic LEL sensor contains a flame arrester that blocks large molecules. This “tremendously underestimates the amount of diesel vapour or jet fuel vapour or turpentine or kerosene,” Henderson says. Very high concentrations of H2S, tetraethyl lead and phosphorus-containing substances can also “rapidly harm” the sensor.
INTO INFRA
By contrast, an infrared sensor is highly effective against large molecules such as jet fuel, diesel or gasoline. Reeves reports that infrared sensors are also often used to measure the combustible levels of carbon dioxide in parts per million (ppm).
Citing settings such as an office boardroom, casino, gym, airport or convention centre, he says that “typically, carbon dioxide would be controlling the fresh air dampers, making sure there is enough proper air.”
Unlike catalytic bead sensors, an infrared sensor looks for the presence of gas by measuring the absorbance of the carbon-hydrogen bond in a combustible gas molecule and does not detect the molecule by burning or consuming it, Henderson explains. “That means that you don’t need the presence of oxygen, the sensor cannot be poisoned and that the sensor can be used for high-range measurement as well as LEL range.”
A standard catalytic sensor, on the other hand, is very easy to poison, requires the presence of oxygen to detect gas and cannot be used for high-range measurement “unless you use a dilution adapter or some means to introduce fresh air into the sample stream,” Henderson points out.
That is not to say the infrared sensor is problem-free. “Where most people get tripped up is the fact that they don’t recognize or don’t understand that those sensors don’t detect hydrogen,” Wagner suggests. Cost is another liability, Henderson adds. “Instead of an instrument being $700, the instrument is going to wind up being $1,700 or $1,800.”
Although it came out with great fanfare five or six years ago, “people quickly shied away from it and went, ‘Well, it’s nice, but if we don’t really need to be selective to methane, why wouldn’t we want a general catalytic sensor that would pick up any combustible gas?’” Reeves asks.
For workplaces where H2S or sulphur dioxide (SO2) may be present, it is worth noting that the American Conference of Governmental Industrial Hygienists (ACGIH) in Cincinnati recently proposed changing the threshold limit value (TLV) for H2S from 10 ppm to one ppm, and from two ppm to 0.025 ppm for SO2.
“Some manufacturers are unable to, at this time, produce instruments where you can set the alarm at the new limits,” says Henderson, while several other manufacturers say their instruments can be adjusted to trigger the alarm at the new limits.
One difficulty with the proposed levels is the lack of uniform requirements. For example, in Nova Scotia, the current published TLV is immediately incorporated by reference into regulations, Henderson points out, but not in other provinces like Alberta where H2S is common in the oil and gas industry. There has been “quite a bit of pushback because there [is] an immense number of instruments out there that cannot be used [with] alarms set at the new limit,” he says.
Industrial Scientific’s Dave Wagner contends that it is impossible to enforce the new TLVs, particularly for SO2. “It’s questionable whether you can detect to those levels, so it’s not practical to try and enforce to those levels.”
Besides lower TLV levels, some workplaces may also require gas detectors that accurately compensate for temperature, pressure and humidity. Gupta points out that in the past, gas monitors could be triggered by not only the presence of gas, but also by high humidity or a drop in pressure. “Now, the sensors will actually compensate for a lot of those things. So they are much more reliable and you get a lot less false alarms,” he says.
Sensors are even getting into plug-and-play technology. Previously, when a user changed a sensor, the gas monitor had to be recalibrated. “Now, the sensors are pre-calibrated, so you can literally unplug the old sensor and plug in a new one and you’re ready to go,” Gupta adds.
BUMP IT UP
Regulations in many provincial jurisdictions that require a “bump” test — checking a gas detector before each day’s use — were previously frustrating for a lot of users, Gupta reports. “They don’t like doing [the test] because it’s extra work for them and they don’t understand the purpose of it.”
Some bump test stations now automatically perform the test, with monitors capable of calibrating themselves and redoing the bump test if it fails, he adds.
“Gas detection used to be very difficult and a bit of a science as well,” Gupta says. Workers need to be trained on how to do bump tests, calibrate and how to build the unit if there is any problems or issues. “It is getting much easier and much better to use and because of that, there is a much better buy-in from users,” Gupta says.
But not everyone has done so. Gupta cites the example of some delivery drivers whose CO monitors continually went off because their vehicles were left idling while they completed deliveries. “It was very irritating for them and they thought there was something wrong with them,” Gupta says of the monitors. “They actually turned the units off because they were so frustrated by the warnings, but it was actually doing its job.”
Don Galman from Honeywell Analytics says that users sometimes see the warnings as a “nuisance alarm,” but turning off the device can expose a worker to harm. He says he has heard of incidents where workers turn off gas monitors to take a smoke break or let their car idle. “These, of course, are the kind of practices we are trying to discourage.”
Galman says his company offers products featuring a green LED light that flashes every few seconds as visual verification that a sensor is working properly. Sometimes, monitor training can be perceived as difficult, he says, with the outcome being that users can be unfamiliar with how a monitor works and why it should always be kept on.
Nonetheless, technological advancements over the years are helping with ease of use, industry experts say. For example, data logging capabilities, typically used by a safety manager or hygienist “who needs this kind of documentation to make informed decisions about worker safety and the purchase of equipment,” are improving, Galman says.
“What the industry is doing with the data logging is automating the process to make the information easier to obtain and it generates the reports almost automatically now. They are more customizable and user-friendly,” he adds.
Microprocessors that have become more powerful and cheaper are allowing gas detectors to do a lot more, Reeves notes. With data logging, they are now easier to interface with computers and allow for more massaging of the information.
Although sensors themselves have not changed that much over the last decade, Reeves says, they are lasting longer. Electrochemical sensors, for example, used to last only a couple of years, but can now easily last five years.
“Oxygen is probably the worst of the lot; there are a lot of oxygen sensors that only last a year or two years,” says Gupta, adding that Draeger Safety Canada will warranty its sensors for five years.
Wagner speculates that the biggest continuing trend will be the use of wireless equipment for real-time detection. This means a manager may be able to track gas concentrations on portable monitors carried by workers in remote areas. If an instrument goes into alarm, others are alerted in real-time instead of the current practice of uploading the data onto a computer after the fact.
“The idea is to make the gas monitors so smart that even if the users don’t know how to work them, they’ll still be serviced by them, maybe their lives will be saved,” Galman says.
Jason Contant is editor of CANADIAN OCCUPATIONAL HEALTH & SAFETY NEWS.
Sidebars
Tipping Point
Flammable gases become more dangerous when they have a relatively low explosive limit, while flammable vapours are more dangerous when they have a relatively low flash point, notes Draeger Safety Canada Ltd. in Mississauga, Ontario. Below is a list of some flammable gases and vapours, and their ignition temperatures.
Substance Lower Explosive Limit(%Volume) Flash point in Celsius Ignition temperature in Celsius
Acetone 2.5 less than -20 535
Benzene 1.2 -11 555
Ethenol 3.1 12 400
Ammonia 15.4 N/A 630
Methane 4.4 N/A 595
Hydrogen 4.0 N/A 560
Location Counts
The Mine Safety Appliances Company, headquartered in Cranberry Township, Pennsylvania, reports that sensors should be placed in areas where air currents are likely to produce the highest gas concentrations, such as corners or stopping points of moving devices that release gas.
In contrast, sensors should not be placed near radio transmitters or sources such as induction heaters or welding activities, or in locations where airborne particles may coat or contaminate the sensor, like paint booths, says information from the company.
Detectors for gases such as carbon dioxide and heavy hydrocarbons should be placed closer to the ground, with hydrogen and methane sensors placed near the ceiling, the information advises. For carbon monoxide and nitrogen, placement should be according to the air current path, at or near breathing level.
A State of Matter
All gases are potentially dangerous, whether in liquefied, compressed or normal state; it is their concentration that is crucial. If gases do not exist in their familiar and breathable compositions, safe breathing is already at risk.
Gases present three categories of risks:
– risk of explosion by flammable gases;
– risk of asphyxiation because of oxygen displacement and increased flammability due to oxygen enrichment; and,
– risk of poisoning by toxic gases
Without auxiliary tools, workers are unable to recognize these dangers early enough to initiate appropriate countermeasures. With a few exceptions, the nose is an extremely unreliable warning instrument. For example, low concentrations of hydrogen sulphide can be sensed through the typical odour of rotten eggs, but the nose cannot detect the gas in lethal, high concentrations.
Even harmless gases such as argon, helium or nitrogen may become dangerous when a sudden release of these gases displace oxygen, presenting a suffocation risk.
While oxygen concentrations of less than six per cent are known to be lethal, excess oxygen increases flammability and may cause the auto-ignition of flammable materials.
Source: Draeger’s Guide to Portable Gas Detection
