There’s no perfect flame detection system for every application. Matching optical flame detector options – including single wavelengths of UV and IR, integrated UV/IR sensors, and more advanced units that offer triple wavelength IR sensors – to your requirements is everything. If you understand the type of flame to be detected, the environmental conditions surrounding the installation, and the required performance, the choice of flame detection technology becomes easier and the potential for false alarms is decreased.
Almost all flames produce heat, carbon dioxide, carbon monoxide, water, carbon, and other products of combustion, which emit visible and measurable UV and IR radiation. These same emissions from non-flame sources cause nuisance false alarms and plant shutdowns. There are two basic types of these emissions: natural sources including rain, lightning, and sunlight; and man-made sources including artificial light sources, welding, and radiation from heaters and machinery. All types include solar-blind UV; window contaminates; non-modulated IR; and modulated IR sources.
Energy that is constant over time or varies at an extremely slow rate like the IR energy emitted from heaters, lamps, and heat from the sun are described as non-modulated sources of radiation. Additionally, there’s a small amount of IR radiation emitted from all objects which is constantly present in any detector’s field of view. As a result, the majority of flame detectors are designed to only detect modulated IR radiation sources – a key characteristic of flames. Still, the detection isn’t straightforward. False sources include heated emissions, moving lights, signals, or combinations of non-modulating sources being altered by objects moving back and forth in front of them in between the source and the sensor (e.g., vehicles, personnel, or fan blades). This is overcome by the use of multi-bands which can distinguish on the IR spectrum between flames and other sources of radiation.
Outdoor applications must contend with the visible range of sunlight, which covers 0.3 to 0.8 microns. UV detectors generally detect energy below solar emissions (0.185 to 0.260 microns) and can be a suitable choice for outdoor applications because of their extremely fast response and wide field of view; but UV/IR and triple IR options offer higher immunity to potential false alarms from high-energy bursts from reflective surfaces. Safety engineers must also consider the source of the fire when selecting a detector. If the fuel could potentially be hydrogen-based, for example, a specially tuned detector is required. For hydrocarbon-based fires from fuels such as methane and gasoline, multi-spectrum IR detectors are typically the best choice.
Window contamination will negatively affect the detector’s performance and can cause the instrument to go into fault mode. Water droplets, condensation, snow, and ice are powerful absorbers of IR energy that can be delivered in random scales and intensity and are a well-known source to trigger false alarms or faults when combined with modulated energy sources like direct sunlight. UV radiation is also easily absorbed by a range of oils, smoke, carbon, and specific gases. Engineers need to be aware of the presence of vapors such as hydrogen sulfide, benzene, ammonia, ethanol, acetone, and others when selecting a flame detector for their application.
By analyzing your application for these types of potential false alarm triggers, you can let your flame detection expert know all the parameters for an optimal detector selection. If you’re experiencing a lot of false alarms, this may be a good time to review your choice of flame detection technology.
By Chris Duncan, Business Manager, Emerson Automation Solutions
Detecting flammable gas that has the potential to threaten people and property in areas where gas clouds easily disperse is a problem in many applications. This recent case history is a classic example.
A UKCS (United Kingdom Continental Shelf) operator was issued an improvement notice from the Health and Safety Executive after a large volume gas leak went undetected on one of their North Sea platforms. The release had not been picked up by the platform’s existing flammable gas detection system because the gas had been dispersing as soon as it escaped.
The company contacted Emerson for help. The solution was to provide the Incus, an ultrasonic gas leak detector that, while working in conjunction with the existing gas detection system, added another line of defense and provided an early warning when gas releases occurred. Most importantly, it increased the safety of platform personnel.
Ultrasonic gas leak detection uses acoustic sensors to identify fluctuations in noise that are imperceptible to human hearing within a process environment. The sensor and electronics are able to detect these ultrasound frequencies (25 to 100KHz), while excluding audible frequencies (0 to 25KHz).
Unlike traditional gas detectors that measure the accumulated gas, ultrasonic gas detectors “hear” the leak, triggering an early warning system. The sensors respond to sound generated by escaping gas at ultrasonic frequencies. Leak rate is mainly dependent on the size of the leak and the gas pressure. In most facilities, the majority of process noise is in the audible range, while limited ultrasonic noise is generated in normal operation. Highly pressurized gas releases produce ultrasound (25-100 kHz) which the sensors are able to pick up despite the presence of audible noise. Ultrasonic (acoustic) gas leak detection technology has several advantages over conventional gas sensor technologies: it does not have to wait until a gas concentration has accumulated to potentially dangerous concentrations; it does not require a gas cloud to eventually make physical contact with a sensor; and the response is instantaneous for all gas types.
The Incus is ideally suited for monitoring outdoor applications such as on an oil platform. The Incus has been engineered to withstand even the most extreme conditions. Performance is not affected by inclement weather, wind direction, leak direction or any potential gas dilution, with an instantaneous response to all gas types. It is an excellent addition to many safety systems adding another layer of detection to existing technologies.
The Health and Safety Executive subsequently inspected the platform and approved the solution provided, resulting in a very happy customer!
Do you have an application that might require the addition of ultrasonic detection? It might be worth a discussion. Contact us HERE today.
By Edward Naranjo, Marketing Director, Emerson
Gas concentration is one of the most important determinants of a substance’s hazard potential. Flammability, toxicity, and oxygen deficiency are often determined by concentration. For combustible gas detectors, gas concentration is expressed as a volume fraction of combustible gas or vapor in air known as the lower explosive limit (LEL), while for toxic gas detectors, the signal output is read as a percent by volume (% vol.), parts per million by volume (ppm (vol.)), or mass per unit volume. Countries and jurisdictions use different units of measurement to define maximum permissible combustible and toxic gas concentrations in the workplace. The choice of the units to use depends on the chemical and its abundance under ambient conditions. As a result, it is necessary to become familiar with the units used and methods for converting between units of measurement.
Volume and Mole Fractions
Units of volume fraction and mole fractions are frequently used for gas concentration. The most common value fraction is ppm (vol.), defined as the ratio between the volume of a constituent Vi and the total volume Vtotal:
As an example, 10,000 ppm = 1% (v/v) or a volume fraction of 0.01. The volume fraction of a constituent φi is defined as the volume of constituent Vi divided by the volume of all constituents of the mixture Vtotal:
Similarly, the mole fraction of constituent Xi is the moles of a target substance n divided by the total number of moles in a mixture ntotal:
The values of volume fraction and mole fraction are identical under the ideal gas law:
The advantage of volume/volume or mol/mol units is that gas concentrations reported in these units do not change over temperature and pressure. By contrast, atmospheric concentrations like mass per unit volume (ex. mg/m3) decrease as gas is expanded since the component’s mass remains constant as the volume increases.
Mass Concentration Units
Concentration units based on mass include mass fraction (ex. mass chemical per total mass) and mass per unit volume. Like ppm (vol.), mass/mass concentrations are commonly expressed as parts per million, where mi is the mass of constituent i and mtotal is the total mass:
Note: Where a gas concentration is expressed simply as ppm, it is unclear whether a volume or mass basis is intended.
In the atmosphere, it is common to express concentrations of mass/volume air like milligrams per meter cubed (mg/m3). Thus, the United States’ National Institute for Occupational Safety and Health (NIOSH) Pocket Guide for Chemical Hazards reports worker exposure limits in ppm (vol.) and mg/m3. To convert from ppm (vol.) to mg/m3, it is assumed the ideal gas law applies under standard temperature and pressure where MW equals molecular weight:
Note that at standard conditions (p = 760 mmHg, T = 273°K), one mole of any pure gas occupies a volume of 22.4 L.
Another useful formula is one that converts from units of ppm (vol.) to ppm (m) at 760 mmHg and 25°C:
For convenience, NIOSH recommended exposure limits (REL’s) for several toxic gases are shown in Table 1 below.
Table 2 shows the LEL’s of several combustible gases in % vol., ppm(m), and volume fraction.
Last, conversion units for common industrial gases are illustrated in Table 3.
Situations Where Unit Conversions May Be Useful
It is tempting to think that converting units of measurement is hardly necessary. After all, in most countries, combustible gas concentrations are measured either in volume fractions or its derivatives, while toxic gas exposure limits are established in ppm (vol.) or mass volume units. Yet one cannot gauge a gas’ hazard potential without comparing attributes in a common plane. Consider that several toxic gases like ammonia and hydrogen sulfide are combustible. The graph in Figure 1 below showing gas concentration in ppm (vol.) gives a sense of toxic and combustible limits in relationship to one another.
Similarly, most hydrocarbons are harmful long before they are at combustible concentrations. As shown in Figure 2 below, the IDLH is often at approximately 10% LEL. Based on those results, an analysis of hydrocarbon toxicity recommended that alarm levels be set at 10% LEL to protect workers from hydrocarbon narcosis (Gardner 2012).
ISO 10156, Determination of Fire Potential and Oxidizing Ability for the Selection of Cylinder Valve Outlets. 2010. Geneva, Switzerland: ISO.
Gardner, R. 2012. Use of Reciprocal Calculation Procedures for Setting Workplace Emergency Action Levels for Hydrocarbon Mixtures and their Relationship to Lower Explosive Limits. Ann. Occup. Hyg. 56 (3): 326–339.
Hi, I’m Ed Naranjo, and I’m your Analytic Expert today. You probably know that Emerson’s detection products are about securing the safety of people and property. Quickly and reliably. But, who determines the safety of safety equipment?
That was my tricky way of telling you that the GDU-Incus ultrasonic leak detector that you’ve been hearing so much about has now received two important approvals, which verify its safety and appropriateness for its applications. One is the highly respected Det Norske Veritas (DNV) type approval. This DNV certificate further confirms the GDU-Incus is suitable for use onboard marine vessels including liquid natural gas (LNG) and liquid propane gas (LPG) carriers, crude oil tankers, and floating production, storage, and offloading (FPSO) units, all of which can suffer loss of production, or worse, in the event that a gas leak is not detected quickly or at all.
Detecting gas leaks in marine environments is challenging for traditional detectors because they require the accumulation of a gas cloud in order to alarm. Extreme weather and wind on vessels and platforms can prevent a gas leak from being detected, allowing the incident to escalate. Since the GDU-Incus responds to the ultrasound produced by the leak, its performance is unaffected by these conditions. That’s why it’s ideal for marine applications. Receiving this approval means that the detector withstood the rigorous testing required for the DNV certification, which further demonstrates the quality and robustness of the ultrasonic gas leak detector.
On top of that good news, this month, the GDU-Incus adds South Korea Certification – K-Mark – to its impressive list of approvals. The testing was performed through the South Korean Testing Laboratory.
These approvals assure potential users that the GDU-Incus has undergone rigorous testing and has been determined to meet the highest quality standards. These assessment processes are built upon scientific research and recognized by regulators, insurers, and major clients throughout the world. Good news for your safety.
Net Safety has recently joined the Emerson team and is excited about contributing to blog discussions. Here’s a little background on Net Safety and some Q&As relating to its products and capabilities.
Net Safety Monitoring is an industry leader in the design, development and manufacture of fixed flame and gas detection as well as many specialized safety and security products designed for harsh, industrial environments. Its principle applications include all areas of the oil and gas market, mining and minerals, power generation, pulp and paper, and water and wastewater.
Net Safety’s state-of-the-art 38,000 square foot R&D laboratory and manufacturing facility is located in Calgary, Alberta — the heart of Canadian oil country, and home to some of the harshest environmental conditions in the world. It enforces strict quality standards and employs innovative engineering to ensure that all its products perform to the demands of the toughest industrial applications — all certified to global benchmarks for safety and performance.
Question: Where are Net Safety products typically installed?
Safety instruments are all designed for Class 1 Division 1, explosion-proof environments — indoors or outdoors, onshore or offshore. Primarily Oil & Gas applications are where you will find Net Safety instruments, as well as Mining, Petrochemical, Aviation, Power Generation, and Chemical Processing to name a few. Do you have an application where you are having challenges with your existing gas and/or flame detection? Ask us a question!
Question: What is the primary advantage with Net Safety products?
Customers come to us with many flame/gas detection challenges. These typically include overcoming environmental conditions, application performance issues, lowering maintenance and eliminating sensor faults. Net Safety instruments overcome these challenges by providing reliable, stable protection for plant and personnel in even the harshest conditions — with many unique and intuitive features that improve performance, simplify operation and reduce maintenance.
We have identified that low-power consumption and wide voltage ranges are often the most overlooked key components for safety instrument performance in many applications. Significant power-level and fluctuation issues occur in many end-user facilities. These can cause safety instrumentation with narrow voltage ranges and high-power requirements to fail or temporarily go offline. This is obviously a very serious safety issue among operators in which Net Safety instruments provide the most complete and effective solution. All Net Safety instruments have been engineered with the lowest power consumption requirements and the widest voltage ranges available in the market. This provides customers with the most stable and reliable performance available, without compromising the latest technologies and advanced features. End-users also see significant energy cost savings over the life of the instrument. Multiply it by an entire plant installation and compare it against the other leading F&G detection manufacturers and the numbers will surprise you. Would you like more information about the advantages of our low power instrument solutions in your application? Ask us a question!
Question: How do you choose which technology suits a particular application?
Environmental and installation conditions will dictate which gas technology is best suited. On the environmental side, conditions like humidity and temperature are primary factors in determining which sensor technology to utilize; installation conditions are background gases, system design, and the area requiring coverage, to name a few. For flame, one of the most important factors is accurately determining the potential false alarm sources and selecting the appropriate technology, then setting delays and/or voting systems to effectively mitigate any false alarms.
Net Safety Monitoring is very excited to join the Emerson team and, of course, we welcome your questions and inquiries. Over the coming months you will see more contributions from the Net Safety team here on AnalyticExpert.com, and you’ll see our complete line available on the Emerson Process Management website. In the meantime please visit www.net-safety.com to learn more about all our advanced safety solutions.