A high-temperature flame ionization detector (FID) featuring an integrated monitor in a direct-mount enclosure. SNR650’s eliminate the need for installation and maintenance of expensive heat-trace sample tubing.

671, 672, 674, 675

These are now the PrevEx® Flammability Analyzer. See description below.


A colloidal system in which a gas, frequently air, is the continuous medium and particles of solids or liquids are dispersed in it. Aerosol thus is a common term used in connection with air pollution control. Settling velocity is very low so particles stay in suspension for long periods of time.


An industrial strength analyzer for continuous measurement of flammable and some combustible vapors, from 0% to 100% of the Lower Flammable Limit (LFL/LEL).


Provides both quantitative and qualitative measurements of the composition of a mixture or compound. Not necessarily continuously.

Boiling Point

At a given pressure, the temperature at which molecules move fast enough to escape from the liquid surface. Solvents with low boiling points generate more vapor at a given ambient temperature than those with high boiling points. They are said to be volatile and are a high risk to store and handle. Solvents with high boiling points produce little vapor unless they are at an elevated temperature. The fire risk is therefore lower.


The British thermal unit is a traditional unit of energy equal to about 1055 joules. It is the amount of energy needed to heat one pound of water by one degree Fahrenheit.

Catalytic Sensor

A heated platinum coil coated with a catalyst that reacts by changing it’s surface temperature in the presence of combustible vapors or gases. The catalytic sensor performs best when used as an area monitor. It is not well suited for constant exposure to process levels of solvent vapors nor for the measurement of vapor mixtures.


A micro-combustion Analyzer that continuously measures the heating value (Calorific Value) of gaseous streams of industrial processes.


A solid, liquid or gaseous substance made up of very small insoluble, non-diffusible particles that remain in suspension in a solid, liquid or gaseous medium of different matter.


The rapid oxidation of a substance involving heat and light.


The movement of molecules away from a region of high concentration to a region of lower concentration. The term "diffusion" denotes the process by which molecules or other particles intermingle as a result of their random thermal motion. If an enclosure contains two gases, the lighter initially above, the heavier below, they will instantly begin to mingle because of their molecular motion.

Electrochemical Sensor

Sensors that change response with the absorption of substances such as Oxygen, Hydrogen, Hydrogen Sulfide, Carbon Monoxide, Sulfur Dioxide Chlorine, and Nitrogen Dioxide. Used primarily as area monitors.


Characterized by or formed with absorption of heat.


Characterized by or formed with evolution of heat.


Rapid, uncontrolled combustion process, which generates a high temperature, a large volume of gas and a pressure or shock wave.


The FFA had been the industry-standard low-temperature flammability analyzer. Replaced by the PrevEx® model SNR671 flammability analyzers (below).

Flammability Range

Flammable gases/vapors have limits below, and above, which flame propagation does not occur. The volume below which flame propagation does not occur is called the Lower Explosive (or Flammable) Limit (LEL). Below this concentration the mixture is said to be too "lean" for a flame to propagate. The volume of gas/vapor in air above which a flame does not propagate is called the Upper Explosive Limit (UEL).

Flash Point

The minimum temperature at which sufficient vapor is formed near the surface of the liquid to ignite it in the vessel in which it is contained. The lower the flash point, the greater the risk.


The FTA was a high-temperature, explosion proof, direct-mount version of the FFA. It has been replaced by the SNR672, 674 and 675 PrevEx® flammability analyzer (below).


A state of matter, in which the molecules move freely and consequently the entire mass tends to expand indefinitely, occupying the total volume of any vessel into which it is introduced. Gases follow, within considerable degree of fidelity, certain laws relating their conditions of pressure, volume, and temperature. Gases mix freely with each other, and they can be liquefied through compression or temperature reduction.

Heating Value

Also known as calorific value, is the energy density of a fuel – the amount of heat energy released when a given amount of fuel burns.

Infrared (IR) Detector

A sample is passed through a measurement cell where infrared energy is absorbed by the solvent vapor and compared with the energy absorbed in a reference cell containing background gas. 


Lower flammable limit. The concentration at which vapors or gases in air are rich enough to propagate a flame. Sometimes referred to as LEL (lower explosive limit).


Provides a quantitative measurement, not qualitative. It measures continuously a condition that must be kept within prescribed limits. It does not differentiate between compounds.


The National Fire Protection Association develops many US safety standards, NFPA 86 is the standard for the design and safe operation of industrial ovens, dryers and fume incinerators.


The increase in oxygen content of a molecule. If an element combines with oxygen, it is said to be oxidized.


Permissible Exposure Limit Time Weighted Average* The maximum concentration of gas to which a worker may be exposed in any eight- hour period, given a forty hour work week. (*OSHA Regulations, Standards - 29 code of Federal Regulations, Part 1910.1, Tables Z 1-A and Z-2).


A series of flammability analyzers using the flame-temperature measurement technique. They have extremely fast response time and are widely used to monitor the concentration of flammable vapors given off by manufacturing or converting processes. Rated as Class I, Division 2 devices, PrevEx® Analyzers have a well-established reputation as reliable, low-maintenance instruments. They are the standard analyzer supplied by many oven and dryer manufacturers.


To spread from one place to another.


Upper flammable limit. The concentration at which vapors or gases in air are so rich that not enough air remains to support combustion. Sometimes referred to as UEL (upper explosive limit)


Converts a gas or vapor concentration to an electrical signal output. It is a type of "transducer."


Multi-channel monitor/display instrument for catalytic, electro-chemical or oxygen sensors. Mounts either near the sensor(s) or at the user’s control panel. Provides 4-20 mA and digital (RS485, Modbus) output signals. Multiple remote SmartMax II’s can be daisy-chained along a single data able connected to the user’s PLC, DCS or computer.


The substance doing the dissolving, or present as the major component, in the formation of a solution.

Spontaneous Ignition Temperature (SIT)

The minimum temperature to which a hydrocarbon must be heated to promote an ignition, in the presence of air, without the application of flame or spark.

Vapor and Vapor Pressure

Used to distinguish a substance in the gaseous state, but below its boiling point temperature. If a pure liquid partly filling a closed container is allowed to stand, the space above it becomes filled with the vapor of the liquid, which develops a pressure. This vapor pressure increases up to a certain limit, depending upon the temperature, where it becomes constant, and the space is then said to be saturated.

Vapor Density

The weight of a volume of pure gas/vapor compared with an equal volume of dry air at the same temperature and pressure. A gas/vapor with a vapor density greater than 1 may travel at low levels to find a source of ignition. With a vapor density less than 1, the gas/vapor tends to rise. Air currents, temperature gradients and other ambient conditions can affect gas/vapor diffusion characteristics, often more than vapor density.


Volatile Organic Compound. VOC's can be segmented into four chemical families: hydrocarbons, halo hydrocarbons, nitrogen compounds, and oxygen compounds.