Process Safety Definitions

Process safety involves numerous concepts, keywords and abbreviations that are essential for the understanding of the subject. We hope our simplified definitions become your key to understanding process safety in all its forms. There are some long lists that follow – each alphabetical, but for ease of use we’ve broken the lists down by the topics, of: General process safety terms, dust explosions, combustible dust testing, process safety management, process hazard assessment and Hazardous Area Classification – in North America and in Europe. We’ve also highlighted a few key terms.

• Chemical Exposure Limits: Thresholds for the amount and duration of exposure to chemicals, to prevent adverse health effects.
• Emergency Response Planning: Developing plans for dealing with emergencies, including evacuations, medical treatment, and communication strategies.
• Fire and Explosion Protection: Techniques and systems designed to prevent, detect, suppress, and/or protect against the consequences of fires and explosions.
• Hazard Analysis: Identifying potential hazards that can cause accidents or incidents.

What is a SIL level?

• Safety Integrity Level (SIL): A measure of the effectiveness of a safety system to reduce the risk of a specific hazard to an acceptable level.
• Safety Management Systems (SMS): A comprehensive, systematic approach to managing safety, including organizational structures, accountabilities, policies, and procedures.
• Toxic Release Inventory (TRI): A resource for learning about toxic chemical releases and pollution prevention activities reported by industrial and federal facilities.

Studying and mitigating dust explosions in industrial settings require an understanding of specific technical terms and concept. Dust explosions can occur in various industries, such as food processing, woodworking, chemical manufacturing, and metal processing. Here are key technical words that form a regular part of the vocabulary of a dust explosion expert working in this area:

• Active Explosion Protection: Systems that detect and react to an impending explosion in real-time to mitigate its effect. This includes explosion suppression and isolation systems.
• ATEX Directive: European directives that describe the minimum safety requirements for workplaces and equipment used in explosive atmospheres. ATEX stands for Atmosphères Explosibles.
• Autoignition Temperature (AIT): The lowest temperature at which a combustible material ignites in air without the presence of a spark or flame.
• Combustible Dust: Fine particles that can ignite and burn rapidly when suspended in air in sufficient concentration.
• Conductive Flooring: Flooring material that, if grounded, prevents the accumulation of static electricity on any conductive object that is directly placed on it, by allowing charges to flow to the ground.
• Deflagration to Detonation Transition (DDT): A phenomenon where a deflagration (subsonic combustion spreading through a gas or along a surface) accelerates and transitions into a detonation (a supersonic shockwave that compresses and heats the gas ahead of it, leading to combustion).
• Deflagration: A combustion that propagates through a gas or dust cloud at a velocity less than the speed of sound in the surrounding medium.
• Dust Collector: Equipment used to capture dust from the air to reduce the amount of combustible dust present in a work environment.
• Dust Explosion Severity Index (Kst) and Dust Explosion Class (St): Metrics used to classify the severity of dust explosion. The Kst value measures the speed of pressure rise in a dust explosion, while the St classification (St1 to St3) categorizes the explosion risk level based on the Kst value.

Process Safety Management (PSM) involves systematic approaches to managing hazards associated with the industrial processes to prevent accidents, injuries, and catastrophic events. Here are some key terms and concepts central to PSM.

• Asset Integrity Management (AIM): The practice of ensuring that the assets (equipment, processes, technology) are designed, operated, and maintained to perform effectively and safely throughout their lifecycle.
• Bow-Tie Analysis: A diagrammatic method for managing risks by identifying and linking preventive and mitigative controls to hazardous scenarios and their potential consequences.
• Chemical Safety Board (CSB): An independent U.S. federal agency charged with investigating industrial chemical accidents to protect workers, the public, and the environment.
• Compliance Audits: Regular, formal reviews conducted to ensure that the practices and procedures of a facility comply with PSM requirements and to identify areas for improvement.
• Emergency Planning and Response: Developing and implementing plans to manage emergencies that could arise from process incidents, including evacuation plans, emergency services coordination, and communication plans.
• Emergency Shutdown System: A type of safety instrumented system designed to safely shut down a process or operation in response to certain hazardous conditions.
• Human Factors Engineering (HFE): The application of information about human behavior, abilities, limitations, and other characteristics to the design of equipment, systems, and jobs to improve safety and performance.
• Incident Investigation: The process of identifying the root causes of incidents, including near misses, to implement corrective actions and prevent future occurrences.
• Inherent Safety: The principle of minimizing the hazards associated with a process by design, rather than managing them with protective systems and procedures.
• Layer of Protection Analysis (LOPA): A semi-quantitative risk assessment method used to assess and manage the risks of hazardous process operations by determining if existing protective measures are adequate or if additional measures are needed.
• Management of Change (MOC): A formal system to manage changes in processes, equipment, or software to ensure that changes do not introduce new hazards or unknowingly increase the risk of existing ones.
• Mechanical Integrity: Ensuring that equipment critical to process safety, such as pressure vessels, storage tanks, piping systems, relief and vent systems, and emergency shutdown systems, are designed, constructed, installed, and maintained to be safe and reliable.
• Occupational Safety and Health Administration (OSHA): The U.S.federal agency responsible for enforcing safety and health legislation, including regulations specific to process safety management.
• Operating Procedures: Detailed instructions that describe how to safely conduct activities involved in a process, covering startups, shutdowns, normal operations, and emergency handling.
• Permit-to-Work Systems: A formal written system used to control certain types of work that are potentially hazardous, ensuring that all elements of a safe work system are in place before the work begins.
• Pre-startup Safety Review (PSSR): A safety review conducted before the commissioning of a new or modified process or facility to ensure that installations are consistent with design specifications and that all safety systems are operational.
• Process Hazard Analysis (PHA): A systematic assessment of the potential hazards associated with an industrial process. Methods include HAZOP (Hazard and Operability Study), What-If Analysis, and FMEA (Failure Mode and Effects Analysis).
• Process Safety Competency: The knowledge, skills, and abilities required to safely operate, maintain, and manage industrial processes, emphasizing the importance of continuous learning and improvement. Term can be used with Organizational Process Safety Competency, which refers to total competency at a company or facility – which can be assessed, and gaps filled as necessary.
• Process Safety Information (PSI): Comprehensive information on the chemical hazards, process technology, and process equipment involved in the industrial process.
• Quantitative Risk Assessment (QRA): A formal and systematic approach to estimating the likelihood and consequences of hazardous events, used to assess the risk associated with industrial processes and to inform decision-making.
• Risk Management Plans (RMPs): Plans developed to identify, assess, and control the risks of hazardous chemicals being used or produced by an industrial process.
• Root Cause Analysis (RCA): A method of problem solving aimed at identifying the root causes of faults or problems to prevent their recurrence, rather than merely addressing their immediate symptoms.
• Safety Culture: The attitudes, beliefs, behaviors, and values of the organization’s members towards safety. A strong safety culture supports continuous improvement and proactive management of safety.
• Safety Instrumented Systems (SIS): Engineered systems designed to take a process to a safe state when predetermined conditions are violated, such as excessive pressure, temperature, or flow.
• Safety Integrity Level (SIL): A measure of the performance required for a safety instrumented function (SIF) in the context of a process safety system, defining the level of risk reduction provided by the SIF.
• Safety Leadership: The actions and behaviors of individuals at all levels of an organization that influence its safety culture and performance, emphasizing the role of leadership in promoting safety as a core value.
• Safety Management System (SMS) Evaluation: The process of assessing the effectiveness of an organization’s safety management system in terms of policy, objectives, planning, responsibility, accountability, and regulatory compliance.
• Safety Performance Indicators (SPIs): Metrics used to assess the effectiveness of safety management systems, including both leading indicators (which predict future performance) and lagging indicators (which reflect past performance).

Understanding the properties of dust that contribute to explosion risks is crucial for designing safe industrial processes. Several standardized tests are performed to evaluate these properties, helping to inform safety measures and compliance with regulation. These tests are typically conducted in specialized laboratories, such as Stonehouse’s own dust lab, where standards set by organizations such as ASTM International, ISO, or NFPA are strictly followed. To ensure quality and reliability of results, Stonehouse Process Safety Laboratory is accredited in accordance with the recognized International Standard ISO/IEC 17025:2017. This accreditation demonstrates technical competence for a defined scope and the operation of a laboratory quality management systems.

What is a powder resistivity test?

• Powder Resistivity Test: Measures the electrical resistance of a dust sample, providing information about its ability to accumulate electrostatic charge. This is important for assessing the risk of electrostatic discharge as an ignition source.

In the USA, Hazardous Area Classification (HAC) is mandated for identifying and classifying areas where flammable gases, vapors, liquids, or combustible dusts may present a risk of explosion or fire. The classification system helps in the safe selection and installation of equipment in such environment. Below is a glossary of terms specifically tailored to the context of the USA.

What is a Hazardous Area?

• ATEX Directive: While ATEX is a European directive, it is relevant for US companies that export equipment to Europe or that operate in locations where compliance with international standards is required.
• Class I, II, III Locations: Classifications used in the NEC to denote the type of hazardous material present. Class I locations are those with flammable gases or vapors, Class II with combustible dust, and Class III with ignitable fibers/flyings.
• Division System: The method used in the NEC for classifying hazardous areas into two Divisions based on the likelihood of an explosive atmosphere being present. Division 1 is for areas where hazards are expected to exist under normal operation conditions, and Division 2 is for areas where hazards are not likely to exist under normal operation conditions.
• Dust Ignition-Proof: Equipment designed to exclude ignitable amounts of dust or to prevent the exterior surfaces from becoming hot enough to ignite a dust-air mixture.
• Explosion-Proof Equipment: Equipment designed in such a way that it can contain an explosion within its housing and prevent the ignition of an explosive atmosphere surrounding it, suitable for Class I locations.
• Factory Mutual (FM) Approvals: A US-based insurer and research laboratory that tests and certifies equipment and products for use in hazardous locations among other standards.
• Group Classifications: The NEC classifies flammable gases, vapors, and dusts into Groups (A, B, C, D for gases and E, F, G for dusts) based on their explosive characteristics to ensure that equipment used is appropriate for the specific hazardous material.
• Hazardous (Classified) Locations: Areas where fire or explosion hazards may exist due to flammable gases or vapors, flammable liquids, combustible dust, or ignitable fibers or flyings.
• Intrinsically Safe (IS): Equipment that is incapable of releasing sufficient electrical or thermal energy under normal or abnormal conditions to cause ignition of a specific hazardous atmospheric mixture.
• Lower Explosive Limit (LEL) and Upper Explosive Limit (UEL): The minimum and maximum concentrations of a vapor in air below which propagation of flame does not occur on contact with a source of ignition (LEL), and above which the vapor-air mixture is too rich to support combustion (UEL), respectively.
• National Electrical Code (NEC): A widely adopted standard for the safe installation of electrical wiring and equipment in the United States, which includes extensive sections on hazardous areas (Article 500-516).
• Purged and Pressurized Systems: Systems that use a protective gas to prevent the ingress of flammable gases or dusts into an enclosure and to maintain a safe interior atmosphere.
• Temperature Classifications: Ratings given to electrical equipment based on the maximum surface temperature generated by the equipment. The NEC adopts temperature classes (T1 – T6) to prevent ignition in hazardous locations.
• Underwriters Laboratories (UL): A safety certification company in the US that provides product safety testing and certification, including for equipment intended for use in hazardous locations.

• ATEX Directive: A European Union directive that describes the equipment and protective systems intended for use in potentially explosive atmosphereThe name ATEX comes from the French “ATmosphères EXplosibles”.
• Electrical Resistivity: A property of a material that indicates how strongly it resists the flow of electric current.
• Explosive Atmosphere: A mixture of dangerous substances with air, under atmospheric conditions, in the form of gases, vapors, mist, or dust in which, after ignition has occurred, combustion spreads to the entire unburned mixture.
• Flammable Limit (also known as Explosive Limit): The concentration of a gas or vapor (measured as a percentage by volume in air) that represents the limits between which the gas or vapor can ignite or explode when an ignition source is present. These are further categorized as Lower Explosive Limit (LEL) and Upper Explosive Limit (UEL).
• Gas Group: A classification system that categorizes flammable gases and vapors into groups based on their maximum experimental safe gap (MESG) or minimum igniting current (MIC). This helps in selecting appropriately rated equipment for specific hazardous areas.
• Group Classification: Classification of explosive gases and vapors into groups based on their explosive and igniting properties. In the US, these are typically Groups A, B, C, and D for gases, and Groups E, F, and G for dusts. Internationally, gases are classified into Groups I (mines) and II (surface industries), with Group II being further subdivided based on the gas’s explosive properties.
• Hazardous Area: An area in which an explosive gas atmosphere is present, or may be expected to be present, in quantities such as to require special precautions for the construction, installation, and use of equipment.
• IECEx System: An international certification system for certifying equipment for use in explosive atmospheres, operated by the International Electrotechnical Commission (IEC).
• Intrinsically Safe (IS): Equipment and wiring that are incapable of releasing sufficient electrical or thermal energy under normal or abnormal conditions to cause ignition of a specific hazardous atmospheric mixture in its most easily ignited concentration.
• Protection Concept: Techniques applied to electrical equipment to ensure it can be safely installed in a hazardous area. Examples include flameproof (Ex d), increased safety (Ex e), and encapsulation (Ex m).
• Temperature Class: The classification of electrical equipment based on the maximum surface temperature the equipment can reach, ensuring it does not exceed the ignition temperature of the surrounding atmosphere. Temperature classes range from T1 to T6.
• Zone 0 (Zone 20 for dust): An area in which an explosive atmosphere is continuously present or present for long periods.
• Zone 1 (Zone 21 for dust): An area in which an explosive atmosphere is likely to occur in normal operation occasionally.
• Zone 2 (Zone 22 for dust): An area in which an explosive atmosphere is not likely to occur in normal operation but, if it does occur, will persist for a short period only.
• Zone Classification: A system used to classify hazardous areas into zones based on the frequency and duration of the occurrence of an explosive atmosphere. For gases, vapors, and mists, the zones are 0, 1, and 2; for dusts, they are 20, 21, and

• Antistatic Material: A material designed to dissipate static electricity and prevent charge build-up. These materials are used in packaging, flooring, and work surfaces to protect sensitive electronic equipment.
• Bonding: The process of connecting two or more conductive objects together to equalize their electrical potential. This helps prevent electrostatic discharge between the objects.
• Capacitance: The ability of a system to store an electrical charge, measured in farads (F). Higher capacitance means more charge can be stored at a given voltage, leading to greater discharge energy.
• Charge Generation: The process by which static electricity is produced, often through friction, separation, or induction. This can occur in everyday activities such as walking on a carpet or removing clothing.
• Conductivity: A material’s ability to conduct electric current, measured in siemens per meter (S/m). Materials with high conductivity, such as metals, allow charges to flow easily.
• Conductor: A material that allows the flow of electric charge, facilitating the dissipation of static electricity. Metals like copper and aluminum are good conductors.
• Corona Discharge: A continuous, low-energy discharge of static electricity from a sharp or pointed conductor in a high electric field. It appears as a faint glow and is often used to reduce levels of static electricity on materials.
• Dielectric Breakdown: The failure of an insulating material to withstand high voltage, leading to a sudden discharge of electricity. This can cause sparks and damage to electrical equipment.
• Electrostatic Attraction: The force that draws opposite charges together. This phenomenon is responsible for dust clinging to surfaces and the sticking of materials like plastic wrap.

What is electrostatic charge decay?

• Electrostatic Charge Decay: The process by which an accumulated static charge dissipates over time, often measured in terms of time constant or decay rate. Faster decay rates reduce the risk of electrostatic discharge.
• Electrostatic Discharge (ESD): The sudden release of static electricity when two objects with different electric potentials come into close proximity. This can cause damage to electronic components and ignite flammable materials.
• Electrostatic Field: The region around a charged object where its electrical force is exerted on other charges. The strength of the field decreases with distance from the charged object.
• Electrostatic Induction: The redistribution of electrical charge in an object caused by the influence of nearby charges. This process does not require direct contact between the objects, to charge objects, for example (unlike triboelectric charging).
• Electrostatic Potential: The work done in moving a unit positive charge from infinity to a point in space, measured in volts. Higher potential indicates a greater likelihood of electrostatic discharge.
• Faraday Cage: A conductive enclosure that blocks external static and non-static electric fields. It protects sensitive electronic equipment from electromagnetic interference (EMI) and can also be used to make measurements of static electricity on materials.
• Grounding (Earthing): The process of connecting an object to the earth to safely dissipate electrical charge. This is a common method to prevent the build-up of static electricity.
• Insulator: A material that resists the flow of electrical charge, preventing the dissipation of static electricity. Common insulators include rubber, glass, and plastic.
• Ionization: The process of adding or removing electrons from an atom or molecule, creating ions. Ionizers are used to neutralize static charges in various industrial applications.
• Spark: A visible discharge of static electricity originating from a conducting object, often accompanied by light and sound. Sparks can ignite flammable materials in the presence of combustible gases or dust.
• Static Electricity: The accumulation of electrical charge on the surface of an object, which remains until it is discharged. It is commonly generated through friction between materials.
• Static Eliminator: A device used to neutralize static charge on a surface, often using ionized air. It helps to prevent static build-up in sensitive environments. Static eliminators can be active (with a power source or radioactive element) or passive (relying on on an electric field to create neutralizing ions)
• Triboelectric Effect: The generation of static charge when two different materials come into contact and are then separated. The materials become oppositely charged due to the transfer of electrons.