Sierra Monitor Corporation TR-001 User Manual

Technical Reprint TR-001

To minimize risks, a plant-wide gas monitoring system must meet the specific needs of
the facility in terms of system inputs and outputs and data acquisition.

Plant-Wide Gas Monitoring for Risk Control

as monitoring has become an integral part of many environmental protection and safety programs. Because of

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increased attention to risks posed by gas, systems that simply annunciate an alarm condition are no longer

adequate. Gas monitoring programs now comprise employee training, data analysis, multiple alarm strategies,
self-diagnostic system verification, and documentation. Data communication has also become a fundamental
component of system design and operation as well. And finally, environmental factors help guide the program
selection process.

GAS MONITORING RATIONALE

Gas Monitoring is an integral part of environmental protection and safety programs. There are three major
categories of hazardous gases. Combustible gases pose a risk to personnel and facilities through fire or explosion..
Oxygen displacing gases deplete workers' oxygen supply in confined spaces. Toxic gases create both immediate
and long term risks to personnel. Toxic gases are those OSHA and other organizations have defined as hazardous to
human health. They are typically monitored both below and above the threshold limit value (TLV). TLV is an
8-hour time weighted average concentration that is the highest value acceptable as a safe working environment.
System design requirements such as the number of sensors required, sensor placement, and system alarm levels will
vary according to the type of gas.

A properly designed gas risk management program can reduce risk. A successful program needs to first, identify the
hazards at the facility, then assess the risk of a hazardous event to the plant, personnel, the community and the
environment. Next, the program needs to comply with insurance, legal and regulatory req uirements. Also, liabilities
and financial risks need to be evaluated. Finally, the program must incorporate company safety philosophies.

Through such a program you can reduce the risks associated with hazardous gas leaks at your facility. Sierra
Monitor offers products that provide critical data to prompt corrective action before a minor leak becomes a major
event. Information can be retrieved from the equipment display, printed locally or recorded by a computer. This
information aids in evaluating potential hazards in relation to operating practices.

Hazard Identification &

Assessment

Risk to

Risk to

Personnel

Control System
Capability/C ost

Environment

Tradeoffs

Risk to
Fa c ility

Regulations

Ins u r a n c e

Requirements

Laws &

Lia b ility

Decision ,

Control Strategy,

System Selection

Company

Philosophy

Financial

Risks

Risk Reduction

Sierra Monitor Corp. 1991 Tarob Ct., Milpitas, California 95035 USA 408-262-6611, 800-727-4377 FAX: [phone]
Visit our Web Site at: http://www.sierramonitor.com E-Mail: [e-mail]

Technical Reprint TR-001

GAS MONITORING OPTIONS

Gases are monitored with permanently installed (fixed) systems or portable instruments, or by taking samples for
evaluation in a laboratory. Portables and sampling are by their very nature only spot checks and are appropriate
only when the risk is extremely low or fixed instruments are not practical. As a general principle, areas where the
risk is sufficient to justify periodic monitoring with a portable instrument, warrant a fixed system.

Conventional Technology. Fixed gas monitoring systems historically have been reactive systems consisting of a
sensor and a controller. The sensor, which can be mounted remote to the controller, usually transmits an analog
signal proportional to the gas concentration. Principles of detection include catalytic bead, solid­state/semiconductor, electrochemical and infrared.

Performance variables that should be considered for sensor performance include:

• Response speed

• Measurement range

• Resolution

• Interfering gases

• Operating range

• Temperature and humidity effects

• Sensor life span

• Ease and frequency of calibration

• Replacement cost

The gas monitoring system required depends upon the scope of the hazardous gas risk. For applications where the
risk is minor, a simple gas monitor that sounds an alarm when the concentration reaches the setpoint may meet the
need. Applications involving a higher risk generally require continuous output of gas concentration to a display,
printer or other indicating or control device. Sierra Monitor's analog gas sensor modules offer a continuous 4-20 mA
DC output and are available for a wide range of hazardous gases.

In applications with the highest level of risk or where the hazard is present throughout the facility, a smart gas
sensor module such as the IT Series and/or the Sentry Gas Risk Management System will meet the need. With
extensive diagnostic capability, flexible configuration, expandability, microprocessor controls, and the ability to
interface with plant-wide control systems, Sierra Monitor IT Series and Sentry Systems are the choice for plant­wide monitoring systems.

System self-diagnostics on both the IT Series sensors and the Sentry controller and sensors help the user know that
the data they are receiving in reliable and accurate.

Gas exposure data analysis needs to be available to prove due diligence in hazardous gas risk management. This
data can be available either via preformatted reports available with the optional printer for Sentry or via a third party
HMI package resident on a computer. Serial communication and the MODBUS interface enable Sentry and IT
Series sensors to interface with the Human-Machine-Interface (HMI) package that can provide complete data
analysis and information on the operator's computer. Such information would include alarm status, gas
concentrations, alarm setpoints, fault alarms, and more. Hundreds of data points are available from Sentry via the
serial communications port.

Sentry’s ability to accept input from a wide variety of devices such as flame detectors, or other unique gas detectors
provides a complete hazard monitoring system to improve the safety management of the facility.

Sierra Monitor Corp. 1991 Tarob Ct., Milpitas, California 95035 USA 408-262-6611, 800-727-4377 FAX: [phone]
Visit our Web Site at: http://www.sierramonitor.com E-Mail: [e-mail]