Wireless Gas Detection: An Update and Two Case Studies

Wireless gas detection systems are available as stand-alone monitors, rapid deployable systems, self-healing mesh-radio systems and as replacements for traditional fixed or hard-wired systems.

One of the advantages of this generation of wireless gas monitors is the ability to re-broadcast the alarms and data in real time. Wireless system users now can engage remote experts in the same way that doctors working in remote locations can interface with medical center specialists in real time. This real-time data availability has been made possible by advances in secure Internet access and the ability to get data onto the Internet from almost anywhere. Data access has become an operational advantage to distributed safety teams as well as multinational firms.

Interoperability has been improved so that systems used in industrial applications can share data with first responders on an emergency basis. First responders with mutual aid agreements also can share wireless units and data with other responding agencies.

Wireless gas detection has been adopted for some very interesting industrial applications. We will examine two applications of wireless gas detection. The first application is the use of wireless gas detection for hydrogen sulfide detection in oil and gas drilling and exploration. The second application uses wireless gas detection for confined space entry in a coal fired power plant.

MESH-RADIO-BASED GAS DETECTION FOR OIL AND GAS DRILLING

Aaron Chamberlain, the area manager for Oilind Safety, has been involved in the deployment of a mesh-radio-based, toxic gas detection system in the Rocky Mountains. The project started in October 2008 and finished its first phase in the middle of 2009.

This particular gas field has 200 shallow sweet gas wells and nine very deep, high-pressure, sour gas wells that range from 24,000 to 25,000 feet deep. The field produces 330 million cubic feet of gas per day. The primary safety issue on the site was that employees and the local community could be exposed to very high concentrations of hydrogen sulfide (H₂S) gas if there were any valve breaks. The challenge was to streamline the rig-up and rig-down time for natural gas wells while still maintaining safety for personnel and the local community.

This site already had presented serious problems for a fixed gas detection system because it required continuous, 24/7 monitoring. Communications on the site were challenging due to high vibration from equipment and noise levels that ranged from 65dB to 140dB. Temperature extremes ranged from 65 F (daytime) to -35 F (nighttime). Due to the high hazard of the site, all equipment had to be intrinsically safe.

The original fixed gas system was mounted in a pickup truck bed filled with wires on spools. The wires needed to be trenched to each of the well sites and then connected to sensor heads mounted on tripods. The trenching and rigging process could take up to 2 weeks, depending on the size of the site. The fixed system was powered by solar panels that had failures, particularly during wintertime. Other issues with the system depended upon how far you could run the wires for the detectors and faulty alarms due to temperature fluctuations.

The initial wireless system evaluations were first a half-day, then a 1 month deployment. Both tests ran smoothly. The first actual deployment of the wireless, mesh-radio-based H₂S system took less than 2 days, already saving time. Most of this time was spent determining where to use fixed or magnetic mounts for the wireless sensors. After some training and experience, the deployment of the wireless system was reduced down to a matter of hours.

The deployment time saved was more than enough to pay for the entire system. The sensors have been stable over the operating temperature range and there has not been any signal loss from the radios. The entire system of six sensors and the base station controller fit in a single, portable case. The current deployment includes four H₂S sensors on the well site itself, around equipment and personnel, as well as two heads stationed in the camp to protect the employees sleeping and the office people on site. The monitors are calibrated by the system once a week. For back up, six personal, single-gas H₂S monitors were deployed for employees working directly on the drill site.

The biggest benefit on this project was the sensor stability and the reduced rig-up/rig-down time.

WIRELESS GAS DETECTION FOR MONITORING A CONFINED SPACE ENTRY

Rick Block, the president of S&R Environmental Consulting Inc. of Denver, has managed the safety of an epoxy re-coating project inside a “bag house” used to collect the solid waste fly-ash particulates from a coal-fired power plant. The utility had significant safety sensitivity due to an earlier accident at one of their sites, and this project was the first coatings project after the accident.

Because of the prior lethal, flash-over accident, the painting contractor, power plant operator, remote industrial hygienist and on-site safety professionals all wanted access to the alarm and real-time sensor data as well as ongoing confidence in the detection/protection solution.

This site had the potential to become immediate danger to life and health (IDLH) at any point. Workers were required to use methyl ethyl ketone (MEK) to clear the mixing blocks and spraying guns. Other site threats included nitrogen oxides (NO, NO₂), sulfur dioxide (SO₂) and carbon monoxide (CO).

The bag house is a large, compartmentalized, multistory building, normally operating under negative pressure. Each compartment is 20 feet wide by 20 feet high by 40 feet long. The project was to coat the inside of the bag house (while it was still operating) with a plural epoxy coating to increase its life span. Workers were grit blasting and applying plural coating in compartments that are isolated by large poppet valves. Leakage or valve failure could cause the isolated compartments to be quickly flooded with CO and SO₂.

The gas detection solution chosen for this site was a wireless, five-gas monitor with lower explosive limit (LEL), oxygen (O₂), SO₂ and CO detectors, and a photoionization detector (PID) for volatile organic compound (VOC) monitoring. In addition to the site gas monitors, the data was shared over the Internet using a secure proprietary network. This provided unanticipated ancillary benefits, in that all safety managers were all able to see the same date in near real time.

Units were operating 17 hours per day, and were calibrated once a week. The wireless monitors were placed on a catwalk 40 feet off the ground with 20 feet of tubing running from the units into the chamber that was being serviced. Normally, two chambers were serviced at any given time.

The sample tube was placed at worker breathing height using a simple stand. Wireless unit data was validated with hand-held, five-gas monitors configured with the same sensors as the wireless units. Extra sensors and intake filters were stored onsite for easy replacement. Filters generally were changed twice for each 17 hour shift of operation.

There were two alarm incidents while the units were deployed. One was a rise in CO, eventually found to be from the exhaust from a compressor that was operating below the catwalk. The second alarm was from VOCs. This was a difficult alarm to trace as there should not have been any VOCs present. Eventually, this was traced to a solvent that workers were using to free stuck bolts.