Application

Detection Requirement

Health & Safety

Health and Safety instruments are relatively sensitive detectors designed to respond to chemical vapors in the sensitivity range specified by OSHA regulations.  Many health and safety detectors are portable and some are miniature.  A typical portable application would be checking out a storage tank for residue before entering it.  There are also fixed site area detectors and fence line monitors.  A typical area monitor would be a hydrogen fluoride (HF) detector network inside and around an alkylation plant in an oil refinery.

Field Analytical Instruments

This relatively new chemical instrument is used to screen samples in the field, for example an EPA superfund site, for survey purposes or even to plan remediation activities such as removing dirt. These instruments save money by focusing the clean up activity to where it is needed and by greatly reducing the number of samples required to be shipped back to a laboratory.  A good example of a Field Analytical Technique using a chemical detector is an instrumented Cone Penetrometer (CP).  CPs are instrumented rods pushed into the soil at a site undergoing a survey or remediation to detect the presence of contaminants in the soil and ground water.  Testing is made quite easy with the elimination of the requirement to excavate an entire site.

Chemical Warfare Agent (CWA) detectors

CWA detectors can be considered a special case of Health & Safety detectors and there has been much cross pollination between the military and civilian worlds especially after 9/11.  For example portable Ion Mobility Spectrometers (IMS) were turned from laboratory curiosities into CWA detectors through large military programs and eventually found their way into industrial applications.  Conversely the advent of homeland security required that military detectors be useful in detecting industrial chemicals such as chlorine and ammonia.  These Toxic Industrial Chemicals (TICs) were not a military concern prior to 9/11.

Explosives Detectors

This is a relatively recent chemical detector application but has resulted in the installation of many high end detectors.  The application pushes the limits of detector sensitivity.  Events such as airliner bombings have provided a great deal of funding.

Explosive Vapor Detectors

Unlike explosives detectors explosive vapor detectors are one of the original chemical detector applications and go back to early coal mines and sewer maintenance where methane is a problem.   Explosive vapors or gases are only explosive in a range of concentrations in air.  Explosive vapor detectors are designed to alert the operator when the vapor or gas is in the dangerous range.  Many potentially explosive vapors are not particularly toxic so this is a different application.  Early detectors drew a sample into a small sealed chamber and ignited it measuring the temperature change to indicate an explosive environment.

Process Analyzer

Process Analyzers are automated instruments used in a chemical processing plant to adjust the parameters of the process based on real time measurements of the product or intermediates.  These analyzers have an advantage in that they add value to the product and can therefore justify a significant investment to purchase, install, and maintain them.  Process analyzers also greatly reduce the need for onsite chemical laboratories by automating measurements that used to require laboratory analysis.  Many devices considered process analyzers are not chemical detectors per se but estimate boiling points, etc.  One of the original process analyzers was the process gas chromatograph used in oil refineries.

Stack or Continuous Emission Monitor (CEM)

Continuous Emission Monitors are required by USEPA and foreign equivalents to accurately measure the target gases being emitted into the environment.  They are required to be very accurate but there are only a few required in a plant and they can be quite sophisticated.  CEMS can be further broken down into extractive systems which draw a sample from the stack and in-situ instruments which directly measure the effluent in the stack.

Emergency Response

This is a relative new category of instrument which is used to trigger a plant shut down or remediation system.  Frequently electrochemical cells commonly used in Health & Safety applications are adapted for this application but they are a very poor fit because they are subject to false alarms which either may cause an inadvertent plant shut down or worse a catastrophe because operators turn them off or ignore them.

Parameter

Discussion

Performance

Performance includes: sensitivity, linear range, speed of response, and false alarm rate including the ability to reject other gases in the matrix.  Some applications do not require an accurate concentration estimate, for example, chemical warfare agent detection and filter breakthrough but must operate with a complex uncontrolled matrix of coexisting materials.  Some process and Continuous Emissions Monitoring (CEM) applications operate with a very small and well known list of coexisting gases but require superb quantitative accuracy.

Environment

Environment includes: temperature range, humidity including condensing water, shock and vibration, the ability to withstand a drop if a portable instrument.

Reliability

Reliability is a big issue for most chemical detector systems in the field.  An understanding of a new application requires an understanding of the cost of a false alarm and the cost of a misdetection as well as a good understanding of the environment.  For example electrochemical cells are very commonly used inexpensive detectors but care must be taken to ensure that coexisting gases will not cause a false alarm and that the detectors are installed in an enclosure that protects them from drastic temperature changes.  False alarms can trigger expensive and disruptive actions or worse encourage workers to ignore the alarm.

Installation and Maintenance

It is best when evaluating a new application for a detector to consider the facilities available at the site including available power, the availability of various gases such as instrument air or water, mounting requirements.  It is sometimes surprising what is available.  Another big issue is calibration.  Calibration can be difficult and expensive.

Cost

Life cycle cost rather than initial cost is terribly important when evaluating a detector for a given application.  Process Control and filter breakthrough applications are most easily justified because they clearly save the customer money.  Initial cost is more important for other applications.  Life cycle cost includes the initial cost of the detector, the cost to install it, the cost to maintain it and the cost to dispose of it.