Gas Monitoring for Brownfield Site Structures

The “specific conditions” which must be met to receive liability protection in the case of a landfill, have to do with mitigating the environmental effects, plus the potential methane hazard to any structure built on the land. The environmental effects are addressed with membrane and or soil caps, a leachate collection system, retaining walls, groundwater protection measures and methane extraction.

One such development project is iPort12, International Trade & Logistics Center, in Carteret, NJ. Situated on the Rahway River, the landfill received municipal garbage until the mid-1980s.

Groundbreaking design and construction strategies were employed because the new facility is being constructed on top of a former landfill. The work includes pilings to bedrock for structural supports and a landfill capping membrane system. The buildings comprise 1.2 million square feet of warehouse space and offices in two buildings.

Tri-state metropolitan New York demand for distribution space and the uniquely convenient location at exit 12 of the New Jersey Turnpike, adjacent to rail lines, near the Port of Newark (10 miles), Newark International Airport (15 miles), the Holland and Lincoln Tunnels (20 and 25 miles), easily justified the state-of-the-art container warehouse development.

The sheer size of the warehouse structure (more than one million square feet) with 36-foot ceilings and attached offices at both ends requires careful attention to environmental controls and Landfill gas detection to avoid excessive costs while furnishing a safe and comfortable facility in which to conduct day-to-day business operations.

The developer must comply with the Landfill Closure and Development regulations, the Uniform Fire Code, and other consensus codes.

The hazard presented by landfill gas is much different from most industrial gas monitoring in that it diffuses slowly from the closed landfill and is not a sudden release phenomenon from a pressurized pipeline, tank, pump or other process vessel. It is not characterized as a point leak source, since the gas will rise and disperse relatively evenly in response to interior air movement, ventilation and work activity.

A structure on a landfill is not usually an electrically classified hazardous area due to the multiple mandatory methods of protection. First is the landfill closure plan, which includes landfill gas collection and monitoring until the methane is fully dissipated.

Next is the membrane and soil caps for the landfill that significantly reduce methane propagation, which is further mitigated by crawl space or slab ventilation for the structure. The interior combustible gas detection system with the HVAC and interior ventilation systems complete the building protection.

Sensidyne was involved early in the iPort12 project to help design a cost effective solution with the highest reliability and lowest cost of ownership. This involved developing a monitoring strategy in compliance with state codes and regulations, equipment selection, installation considerations, system commissioning and maintenance functions.

Since methane is lighter than air, it can collect in the high points of the warehouse, under the roof, and this is a concern. The offices at either end of the building will have enclosed spaces where methane might collect, and these must be monitored as well. The crawl space or slab ventilation systems may also be monitored for vent activation or control purposes.

The choice of sensor technology was clear. Point Infrared hydrocarbon detectors would be used due to their long life, very low maintenance needs and security integrity level. The Sensidyne Detectors are FM performance certified and approved intrinsically safe. This enables the sensor to be installed remote from the transmitter (high in this case) using 4-conductor low voltage cable, thereby reducing the installed cost.

A remote gassing fixture is employed to simplify the annual maintenance procedure.

An important point: Infrared hydrocarbon sensors cannot be poisoned by caulk or paint fumes, which render Catalytic bead-type sensors useless. The Sensidyne point Infrared hydrocarbon sensor always fails safe.

Catalytic type sensors must have gas applied monthly to prove operation and offset aging effects.

SensAlert PLUS has other unique user benefits such as displayed “Sensor Life Remaining,” optional HART or Serial Communications and Alarm Relay Options.

One transmitter recognizes and accepts all Oxygen, Toxic and Combustible sensors.

With a real-time clock onboard, the Calibration record, TWA alarm and other data is time stamped and available for viewing or via the communications interfaces. SensAlert PLUS can be installed in any hazardous classified or unclassified area. A large backlit LCD display and non-intrusive user interface complete the transmitter.

Deploying sensors along the ceiling of the huge structure presents installation, maintenance and cost difficulties due to the required configuration and number of sensors. A better solution for the warehouse area is SenseLine, a laser-diode based open path gas detector from Senscient, a Sensidyne technology partner.

Senscient, Inc. has collaborated with Sensidyne, Inc., a major gas detection and health & safety products maker, to distrib ute SenseLine, a revolutionary Open Path Gas Detector (OPGD), in North America. OPGD, utilizing NDIR (non-dispersive infrared) detection techniques, has been in use since the late 1980’s and is so widely accepted for Oil, Gas, Petrochemical and other industry’s combustible gas detection, that there is a recently approved performance standard.

In order to address present non-dispersive infrared OPGD shortcomings of resolution, accuracy, calibration and maximum path length, Senscient is introducing their ELDS technology open path gas detector, based on laser diode spectroscopy.

Using Fourier transform and harmonic fingerprint technology, ELDS virtually eliminates coherent noise and false alarms. This significantly enhances the resolution over the path length for up to three orders of magnitude improvement over existing open path NDIR devices. ELDS provides these unique benefits and advantages.

• ELDS based Open Path Gas Detection systems provide reliable, sensitive detection of flammable gases at low ppm concentrations.

• ELDS-based OPGD systems offer three orders of magnitude in increased sensitivity for hydrocarbons, greatly increasing the probability of detecting a flammable gas leak before it reaches catastrophic proportions.

• Unique Simu-Gas feature provides the long sought-after ability to accomplish remote, on command, electronic functional testing of open path gas detectors either locally or from the control room.

Senscient uses Simu-Gas for the simplest and most reliable gas detector functional test available. In an ELDS system with Simu-Gas, the transmitter’s microprocessor has direct control of the synthesis of the laser diode drive waveforms, and access to the Harmonic Fingerprints being produced by the absorption of laser diode radiation from the retained sample of target gases.

Upon receiving a command instruction, the transmitter’s microprocessor adds Harmonic Fingerprint components to the laser diode drive waveforms to simulate the presence of a given quantity of target gas in themonitored space. The optical radiation leaving the transmitter then faithfully simulates the presence of target gas in the monitored path.

When the receiver processes the signal that it is receiving from the transmitter, it sees the Harmonic Fingerprint components and outputs the corresponding quantity of target gas. By simply comparing the gas reading output by the receiver to the quantity of target gas that the transmitter was instructed to simulate, the correct operation of the gas detector is verified. As with Infrared point hydrocarbon detectors, the Senscient ELDS open path gas detector always fails to safe.

Due to the gradual but persistent nature of the landfill gas hazard and its dispersion characteristics in the Warehouse, the ELDS open path detector will be used to shoot the length of the warehouse near the ceiling high point. This gas measurement is proportional to the average methane concentration over the path length (warehouse length). Its output signal will go to a digital gas detection controller, capable of powering, communicating with and interpreting the signals of up to 16 gas detectors. The remaining inputs will be from the office area’s Point Infrared hydrocarbon detectors.

The final number and installation locations will be determined once a tenant decides on the office layout.

The final gas detection system layout for the warehouse and two office areas depends upon tenant office configuration, building inspection and Fire Marshall Approvals.

Gas monitoring safety systems are often modified to address owner and tenant changes, landfill or gas survey data and requests by the inspecting authority.

A one-line drawing of the suggested gas detection system layout is available upon request. The design is very flexible, incorporating spare capacity for future needs such as monitoring CO and NO2 from Diesel engine or lift truck exhaust, as well as adding Infrared Hydrocarbon sensors for the much smaller Southwest structure, once its interior layout is decided.