Hydrogen, a combustible gas, is colorless, odorless, tasteless and non-toxic, but hydrogen is ranked highest on the National Fire Protection Agency (NFPA’s) flammability scale because it is flammable if even small amounts are mixed with air. Low concentrations of toxic gases such as ammonia can trigger coughing and nose and throat irritation, while high concentrations cause immediate burning of the eyes, nose, throat and respiratory tract, and can result in blindness, lung damage or death. Chlorine, though not flammable alone, can react explosively or form explosive compounds with other chemicals such as turpentine and ammonia.
These and myriad other combustible and toxic gases are found in industrial processing and manufacturing settings — whether they are used in the actual processing or are byproducts of processes. That’s why industrial plants need a gas detection network to mitigate risk in all areas where combustible or toxic gases could create a workplace hazard for life safety.
Gas Detection and Notification
Techniques for Risk Mitigation
Life safety gas detection systems require not only the ability to detect leaking combustible or toxic gases — but also to mitigate risk through action.
According to IEC 60079-29 Series standards and IEC 62990 Series standards under development, a life safety gas system does more than detect the presence of combustible and toxic gases. It must be able to provide alarm notification if data from the gas detectors hits a certain threshold. It must also have the ability to take corrective actions such as increasing ventilation, closing a valve or door, or de-energizing equipment to mitigate risk.
In life safety systems, gas detectors tend to have feature-rich displays as well as smart capabilities that improve digital information transfers. The gas detectors are connected to a safety system controller (SSC) and various other devices that can take a number of different actions in order to help bring a dangerous situation back to a safe state.
The SSC for risk mitigation systems receives and interprets input from multiple gas detectors and decides whether or not some action needs to be taken. In order to prevent nuisance alarms, the SSC may discount information from a single detector if it is not confirmed by data from other detectors in the same area. The SSC must be IEC 60079-29 Series and/or IEC 62990 Series compliant as applicable to ensure that signaling, control, notification, and activations can be depended upon for life safety during adverse conditions.
Portable and transportable gas detectors will further mitigate personnel risk by ensuring full detection coverage in all areas of the workplace.
Risks of Combustible and Toxic Gases
Combustible gases are those that can cause a fire or explosion if the gas is exposed to an ignition source such as a spark, a hot surface, an open flame or even friction caused by gas escaping through a pipe fissure. Combustible gases include hydrocarbons and hydrogen.
A toxic gas can cause harm to humans, ranging from minor irritation to death. Toxic gases include, but are not limited to, hydrogen sulfide, carbon monoxide, nitrogen dioxide, ammonia and chlorine. Even at low concentrations measured in parts per million, certain toxic gases can cause death by poisoning caused by exposure to carbon dioxide or by asphyxiation. Many gases are both combustible and toxic.
From a risk mitigation perspective, there is a hierarchy of risk that should be considered when designing a plant’s hazardous-area gas detection system. The “Risk Mitigation” chart above ranks the risk mitigation objectives in priority order, and describes the type(s) of gas detection required for each objective.