Photoionization Detectors

Better known as PIDs, these flame sensors are highly specialized and use high-energy photons to break down ions into charged particles. Afterwards, compounds can then conduct electrical currents to measure how many parts per million, or PPM, are present in the air. Very precise and efficient, these detectors are becoming widely used within the oil and gas industry, wastewater treatment plants, and chemical processing facilities.

Multi-Stage Detection Systems

Because the risks associated with benzene are so high, most facilities use multi-stage detection systems to help alert workers to dangerous situations. When these systems are in place, industrial flame detectors are able to measure the concentration of certain aromatic compounds in the air, but are then able to break down the measurements to determine whatever benzene levels may be present. Also viewed as being extremely accurate and reliable, these systems allow for very precise readings in the harshest of work environments.

Portable Benzene Detection Monitors

Since there are many instances where benzene levels can become very high in confined spaces, more and more companies are now providing their maintenance personnel and other workers with portable benzene detection monitors. Widely used in refineries, manufacturing facilities, and offshore oil rigs and platforms, these industrial fire detectors are considered essential equipment for those working in confined spaces and in isolated areas where help may not be immediately available in the event benzene levels reach dangerous levels.

Fixed Benzene Detector Systems

In refineries, pipelines, or other industrial facilities that may be large in scale, installing fixed benzene detector systems may be the most effective way to detect dangerous levels of benzene. By strategically placing these units in various areas within a facility, benzene levels are able to be monitored 24/7.

Speak with GDS Experts

Since technology continues to evolve when it comes to benzene detection methods, it’s important to work with experts who have the knowledge and experience needed to recommend the best system for your facility. To accomplish this, contact an Applications Engineer at Global Detection Systems and let them provide answers to your most complex questions regarding benzene detection methods.

Why Do Some Instruments Block Negative Readings?

If you have not come across a negative reading on your benzene monitor, it is probably likely that the manufacturers blocked the negative readings from getting displayed. When the gas concentration is negligent, the gas monitor will show zero reading, even if it is supposed to display a negative reading. This is done to avoid alarming users when there is a low level of gas in a facility, such that it will not cause any harm or danger.

Dave Wagner said in a recent article:

“Customers sometimes will say that they have never seen a negative reading on an instrument before but that they recently changed monitors and now seem to see them all the time. This observation is because some instruments block negative gas readings from appearing on the instrument display, showing all negative readings as zero.

This practice can serve to keep you from seeing and recognizing the hazards that exist.”

How To Avoid Negative Readings

If you find your gas monitor showing negative readings successively, you need to make a ‘fresh air adjustment.’ To do this effectively, get the instrument out in fresh air that is devoid of any contaminants and allow the sensors to get normalized. The time taken for this ‘warming up’ of the sensor varies for different types of sensors. While pellistor-type LEL sensors take 6-8 minutes to stabilize, electrochemical sensors can sometimes take up to an hour to stabilize.

According to a recent article:

“To avoid problems make sure the instrument is located in fresh air that does not contain measurable contaminants, and give the sensors time to stabilise completely before using the instrument or making a fresh air adjustment.   Remember that stabilisation can sometimes take quite a bit of time. While pellistor type LEL sensors usually stabilise completely within 6 – 8 minutes, electrochemical sensors that have been exposed to certain interfering contaminants can sometimes take an hour or longer to clear completely.”

Then make the fresh air adjustment. This will help the sensor to detect even low concentration of gases effectively.

Seeing negative readings on your gas monitor? Know what you can do about it. Pay attention to rising gas readings and take appropriate steps to re-set the gas monitor. This will allow you to ensure safer working conditions at industrial facilities and chemical plants.

The industrial user has the following choices of real-time benzene monitor:

RECOMMENDED:

Photoionization detectors (PIDs) with pre-filter tubes: Photoionization involves exposure of a gas sample to ultraviolet light. The excited molecules lose electrons to become positive ions, and the current resulting from movement of these ions is detected. The pre-filter removes molecules that would also ionize and result in a false positive signal. These can allow continuous, real-time rapid monitoring of very low concentrations of benzene with a high degree of precision.

Photoionization detectors (PIDs) incorporated into gas monitors: Rather than a pre-filter, competing technology uses infrared absorption to simultaneously monitor for benzene and other gases of interest. Sensitivity is excellent.

NOT RECOMMENDED:

Multi-gas monitors: These machines are designed to detect volatiles present at levels posing a hazard for explosion. They will not detect concentrations of benzene at lower levels and as such cannot be used to monitor compliance with applicable safety regulations.

Colorimetric gas detection tubes: These are sampling tubes impregnated with a reagent that reacts with benzene to give a color change. Sensitivity is acceptable. However, industrial use requires a monitoring system with an alarm. Although this method could be used as a double-check on a monitor, the tubes expire, and waiting to ship a fresh batch of tubes before double checking an important safety monitor is not acceptable.

Portable gas chromatography (GC) systems: GC provides sensitive and specific measurements of benzene. However, they are large and heavy, and they require a highly trained technician to operate. Perhaps useful to double check a spot flagged by real-time monitors (if the technician can get the machine into that spot), but not practical as a stand-alone approach.

Metal oxide-based sensors: Old technology, they are sometimes used because they are cheap. However, they are not sufficiently sensitive to monitor compliance with safety regulations. They also aren’t specific for benzene and environmental conditions will affect readings.

Compact mass spectrometer (CMS): These units do measure benzene to 0.5 ppm, but that is not nearly as sensitive as other methods used for safety regulation compliance. Hand-held monitors are not yet commercially available as they are with some other options; the requirement for cartridges can add to cost.

Sampling followed by off-line chemical analysis methods can be required for regulatory compliance. One method is standard:

Gas chromatography with mass spectrometric detection (GC-MS): Gas is either sampled directly or pumped through an adsorbent and subjected to standardized, laboratory-based analytical procedures. This technique is the gold standard for quantifying benzene, but readings will take hours (if laboratory is onsite) or days (if offsite).