Fire & Gas Detection System
Introduction
Gas detection systems, often referred to as Fire and Gas Systems (FGS) in industries like oil and gas and petrochemicals, and Life Safety Systems (LSS) in sectors like semiconductor and marine industries, play an essential role in identifying hazardous gases and ensuring safety in high-risk environments. These systems are responsible for detecting harmful gases, initiating alarms, and, in some cases, triggering automated safety responses, including shutdowns.
Given the complexity of modern production facilities, especially in semiconductor, photovoltaic, oil and gas, petrochemical, and marine industries, these systems must be designed meticulously, regularly maintained, and calibrated to ensure continuous protection. This application note provides a detailed overview of the critical factors to consider when designing and maintaining gas detection systems, focusing on gas risk identification, industry standards, sensor technologies, alarm verification, and the importance of ongoing calibration and maintenance.
1. Identifying Gas Hazards in Different Industries
Each industry faces unique gas hazards based on the nature of its operations: Oil and Gas / Petrochemical Industries: The risks typically stem from combustible gases like methane, propane, and hydrogen sulfide. These gases are often flammable and toxic, requiring reliable detection systems to prevent fire, explosions, and exposure risks.
Semiconductor / Photovoltaic Industries: The use of specialty gases such as silane, phosphine, and arsine presents hazards due to their toxicity, reactivity, and flammability. These gases can cause catastrophic damage if not adequately monitored. As described in the survey, incidents involving silane explosions in semiconductor facilities have resulted in severe damage, loss of life, and extended production downtime.
Marine Industry: In marine applications, hazardous gases like methane, carbon dioxide, and hydrogen sulfide present risks, particularly in confined spaces such as engine rooms and cargo holds, where flammable and toxic gas buildup can occur.
In each of these environments, studying the Material Safety Data Sheets (MSDS) for each gas is crucial for understanding its specific hazards, including flammability, toxicity, and environmental impact. Silane and Chlorine Trifluoride (ClF3), commonly used in semiconductor facilities, are particularly hazardous due to their high reactivity and toxicity. Silane is known to cause spontaneous explosions, while ClF3 reacts with water or moisture to produce highly corrosive acids.
2. Compliance with Industry Standards and Regulations
Gas detection systems must comply with various safety standards and codes to ensure reliability and safety. These regulations vary across industries:
Oil and Gas / Petrochemical Industries: Common standards include NFPA 70 (National Electrical Code) and NFPA 72 (National Fire Alarm and Signaling Code), as well as API RP 14C for Fire and Gas Systems in offshore facilities. IEC 60079 and ATEX govern equipment used in explosive atmospheres.
Semiconductor / Photovoltaic Industries: Safety codes such as SEMI S2 and NFPA 318 regulate the design and operation of gas detection systems in fabrication plants. These standards address the hazards of toxic gases like arsine and phosphine, which are commonly used in wafer fabrication.
Marine Industry: SOLAS (Safety of Life at Sea) and IEC 60092 govern fire and gas safety on vessels, ensuring systems meet stringent safety requirements for handling hazardous materials at sea.
These standards provide comprehensive guidelines for designing, installing, testing, and maintaining gas detection systems, ensuring they perform reliably in hazardous environments.
3. Understanding Gas Characteristics and Setting Alarm Points
A deep understanding of the chemical and physical properties of the gases used is essential when designing gas detection systems. Each gas presents unique detection challenges:
Flammability: Combustible gases such as methane and propane require detection systems capable of identifying concentrations far below the Lower Explosive Limit (LEL) to prevent explosions.
Toxicity: Gases like hydrogen sulfide, carbon monoxide, and chlorine can be lethal even at low concentrations. Therefore, setting alarm points based on the Threshold Limit Value (TLV) and Time-Weighted Average (TWA) is essential to prevent toxic exposures.
Reactivity: Highly reactive gases like silane and chlorine trifluoride require specialized detection technologies to ensure that small leaks are identified before catastrophic reactions occur.
Alarm points should be configured to provide early warnings at low concentrations (TWA) and immediate action at higher, dangerous concentrations (TLV or a percentage of LEL).
4. Selecting Sensor Technology
Selecting the right sensor technology is critical to ensure accurate and reliable gas detection. Each type of gas requires a specific sensor to prevent cross-sensitivity and false alarms, which can lead to unsafe conditions if alarms are ignored.
Common Gas Sensor Technologies: Electrochemical Sensors: Primarily used for detecting toxic gases, these sensors produce a current based on a chemical reaction with the gas. They are commonly used for hydrogen sulfide, carbon monoxide, and chlorine detection.
Metal Oxide Semiconductor (MOS) Sensors: MOS sensors, while fast in response, are prone to cross-sensitivities, particularly with solvent vapors. However, advanced proprietary filters can improve selectivity for specific gases like methane.
Infrared (IR) Sensors: Effective for detecting gases like carbon dioxide and methane, these sensors use the absorption of infrared light to determine gas concentration. IR sensors are highly reliable in environments where electrochemical or MOS sensors may be prone to interference.
Photoionization Detectors (PID): Used for detecting volatile organic compounds (VOCs), PIDs ionize gas molecules and are highly sensitive to gases like acetone, benzene, and ammonia.
Selecting the appropriate sensor technology requires careful consideration of the environment, the gases present, and the potential for interference from other chemicals.
5. Gas Alarm Verification
Gas alarm verification is a critical process that ensures the alarms triggered by the detection system are accurate and valid. When an alarm is triggered, operators should use portable gas detectors to confirm the presence of the hazardous gas.
Unfortunately, many operators are not adequately trained in selecting the correct portable detectors for verifying specific gas alarms. This lack of training can result in the assumption that alarms are false, leading to dangerous behavior where operators ignore alarms entirely. Over time, this can condition operators to dismiss alarms, even during actual gas leaks, which may lead to catastrophic events such as fires or explosions.
For effective gas alarm verification, it is essential that:
Operators are trained to understand which portable detectors to use based on the gas in question. Portable detectors are properly maintained and calibrated, just like fixed systems. Gas detectors are checked regularly to prevent misreading or malfunction. Alarm verification protocols should include clear instructions for selecting and using portable detectors to avoid the dangers of misinterpreting gas alarms.
6. Maintenance and Calibration
The reliability of a gas detection system depends heavily on regular maintenance and calibration. Gas sensors degrade over time, and their accuracy declines as they are exposed to environmental factors and gas concentrations. Periodic calibration ensures that the sensors maintain their accuracy and can reliably detect hazardous gases.
Sensor Calibration: Gas sensors should be regularly calibrated using standard gases to verify their accuracy. Calibration intervals vary depending on the sensor type and application environment but should be conducted at least semi-annually or according to the manufacturer’s guidelines.
Sensor Replacement: Gas sensors are consumable and must be replaced periodically to maintain system functionality. Extended use beyond their expected lifespan can result in false alarms or, worse, failure to detect hazardous gases, creating significant safety risks.
In semiconductor and photovoltaic industries, gas detection systems rely heavily on predictive maintenance techniques to ensure sensors are replaced before they fail. This proactive approach helps prevent production downtime and ensures continuous protection from hazardous gases.
7. Human Error and Training
As discussed in the survey, human error is a significant factor in industrial accidents related to gas detection systems. A lack of adequate training, overworked staff, and improper handling of gas detectors during maintenance or alarm verification can lead to dangerous situations. It is critical that operators are provided with sufficient training on:
Selecting and using the appropriate portable gas detectors. Verifying gas alarms accurately. Performing routine maintenance and calibration correctly to prevent sensor drift or failure. Training programs should also emphasize the importance of not dismissing alarms as false without proper verification, as this behavior can result in catastrophic consequences.
Conclusion Designing and maintaining gas detection systems in hazardous environments, such as those in the oil and gas, petrochemical, semiconductor, and marine industries, requires a deep understanding of gas hazards, appropriate sensor selection, and regular maintenance. Adhering to industry standards and ensuring accurate alarm verification processes are essential for preventing industrial accidents and protecting both personnel and facilities. Proper training and alarm verification protocols, along with timely calibration and maintenance, ensure that gas detection systems remain effective and reliable, providing critical protection against the inherent risks of hazardous gases.