Inherent Safety
A concept or an approach to safety that focuses on eliminating or reducing the hazards associated with a set of conditions.
Inherently Safer
A condition in which the hazards associated with the materials and operations used in the process have been reduced or eliminated, and this reduction or elimination is permanent and inseparable.
Inherently Safer
A condition in which the hazards associated with the materials and operations used in the process have been reduced or eliminated, and this reduction or elimination is permanent and inseparable from the process. Inherently safer technology (IST) is also used interchangeably with inherently safety in the book.
Inherently Safer Design
A way of thinking about the design of chemical processes and plants that focuses on the elimination or reduction of hazards, rather than on their management and control.
Inhibitor
A chemical which is added to another substance to prevent an unwanted chemical change from occurring. Importance: Inhibitors are sometimes listed on a MSDS, along with the expected time period before the inhibitor is used up and will no longer prevent unwanted chemical reaction.
Initial List (of incidents)
A list containing all the incidents identified by the enumeration methods chosen.
Initial Pressure
The maximum normal operating pressure that exists at a point in the system prior to initiation of a flame event.
Initialization
Originating or establishing basic conditions or start-up state.
Initiating Cause
In the context of hazard evaluation procedures, the operational error, mechanical failure, or external event or agency that is the first event in an incident sequence and marks the transition from a normal situation to an abnormal situation. Synonymous with initiating event.
Initiating Event
The minimum combination of failures or errors necessary to start the propagation of an incident sequence. It can be comprised of a single initiating cause, multiple causes, or initiating causes in the presence of enabling conditions.
Note: The term initiating event is the usual term employed in Layer of Protection Analysis to denote an initiating cause or, where appropriate, an aggregation of initiating causes with the same immediate effect, such as "BPCS failure resulting in high reactant flow."
Injury
Physical harm or damage to a person resulting from traumatic contact between the body and an outside agency or exposure to environmental factors.
Inoculation
Introducing material (a vaccine, for example) into the body's tissues; also introducing cells into a culture medium.
Input
The current, voltage, power, or driving force applied to a circuit or device. Also called input value of input data. The terminals or other places where current, voltage, power, or device. Also called input terminal. Data which can be ready by the application program from an interface between the user program execution function and another functional unit of the PES. Also called program input.
Input Device
The device or set of devices through which data is brought into another device. A device that reads input quantities (i.e., thermocouple, level switch). Devices such as limit switches, pressure switches, push buttons, etc., that supply data to a PES. These discrete inputs have a common return or an individual return (referred to as isolated inputs). Other inputs (may) include analog devices and digital encoders. Pneumatic, hydraulic, or electronic switches for common input devices such as pressure switches, flow switches, level switches, temperature switches, selector switches, and push buttons. Also see "sensor".
Insolation
Solar radiation heat loading (Watts/m2).
Inspection
A work activity designed to determine if ongoing work activities associated with operating and maintaining a facility comply with an established standard. Inspections normally provide immediate feedback to the persons in charge of the ongoing activities, but normally do not examine the management systems that help ensure that policies and procedures are followed.
Inspection, Testing, and Preventive Maintenance (ITPM)
Scheduled proactive maintenance activities intended to (1) assess the current condition and/or rate of degradation of equipment, (2) test the operation/functionality of equipment, and/or (3) prevent equipment failure by restoring equipment condition.
Instability
The degree of intrinsic susceptibility of a material to release energy through self-reaction (polymerizing, decomposing or rearranging).
Installation
In the context of the EU Seveso Directive (Seveso 2), a technical unit within an establishment in which dangerous substances are produced, used, handled, or stored. It includes all the equipment, structures, pipework, machinery, tools, private railway sidings, docks, unloading quays serving the installation, jetties, warehouses or similar structures, floating or otherwise, necessary for the operation of the installation.
Instantaneous Release
Emissions that are short in duration compared with the travel time (time for cloud to reach location of interest) or sampling (or averaging) time.
Instruction
A programming language Element that specifics an operation and the values or location of its operands.
Instrumented protective system (IPS)
A safety system composed of a separate and independent combination of sensors, logic solvers, final elements, and support systems that are designed and managed to achieve a specified risk reduction.
Insulating
See "nonconductive".
Insulating Flange
A flange or spool piece inserted into an otherwise conductive pipe-hose system. These are not truly insulating but have typical resistances of about 10 kW, which is high enough to prevent hazardous stray currents but low enough to prevent hazardous static accumulation. Used particularly in liquid or vapor lines subject to stray current arcs (break-sparks) when hoses are disconnected.
Integral Model
A dispersion model which averages (or integrates) the concentration in a given dimension or time so that concentrations can be described by solving an ordinary differential equation instead of a partial differential equation.
Intent
A course of action an adversary intends to follow. When assessing threats, security professionals need to evaluate intent as well as capabilities. To determine the intent and motivation of an adversary, an adversary's goals and objectives, as well as specific events that might trigger an adversary's act, must be closely examined. The questions that should be asked about intent are: Does the adversary have a current or projected need for this asset? Does the adversary seek to deny or destroy the use of this asset?
Intentional chemistry
Processing of substances such that a chemical reaction is intended to take place.
Interlock
A protective response which is initiated by an out-of-limit process condition. Instrument which will not allow one part of a process to function unless another part is functioning. A device such as a switch that prevents a piece of equipment from operating when a hazard exists. To join two parts together in such a way that they remain rigidly attached to each other solely by physical interference. A device to prove the physical state of a required condition and to furnish that proof to the primary safety control circuit.
Interlock System
A system that detects out-of-limits or abnormal conditions or improper sequences and either halts further action or starts corrective action.
Intermediate Event
An event that propagates or mitigates an initiating (basic) event during the accident sequence (e.g., improper operation actions, failure to stop an ammonia leak but an emergency plant mitigates the consequences).
Intermediates
Materials from a process that are not yet completely finished product. They may be a mixture or compound.
Intermittency
The fraction of the time that a measured value is zero in a time series of measurements.
Internal
A Watch Dog Timer that is not independent of the Programmable Electonic System it checks.
Internal Boundary Layer
A transition layer rising downwind of a change of surface roughness, which separates the air below, which has adjusted to the new surface, from the air above, which is still influenced by the old upwind surface. The internal boundary layer has an average slope of about 1/100 to 1/10.
Internal Controls
The various engineering and managerial means, both formal and informal, established within an organization to help the organization direct and regulate its activities in order to achieve desired results; also refers to the general methodology by which specific management processes are carried on within an organization. The requirement for management systems and their formal evaluation during an audit are not currently compliance requirements. The evaluation of the adequacy of the internal controls is accomplished using some of the related audit criteria.
Internal Failure
A failure involving either the hardware or the software of the Process Control System, excluding the Application Program.
Interrupt
A break in the normal flow of a system or program occurring in such a way that the flow can be resumed from that point at a later time.
Interview
Questioning, both formally and informally, facility personnel or other individuals in order to obtain an understanding of the plant's operations and performance.
Intrinsic Property
In relation to materials, a property of the material itself, regardless of use or environmental conditions.
Intrinsically Safe
Equipment and wiring which is incapable of releasing sufficient electrical or thermal energy under normal or abnormal conditions to cause ignition of a specific hazardous atmospheric mixture or hazardous layer. A protection technique based upon the restriction of electrical energy within apparatus and of interconnecting wiring, exposed to a potentially explosive atmosphere, to a level below that which can cause ignition by either sparking or heating effects. Because of the method by which intrinsic safety is achieved, it is necessary to ensure that not only the electrical apparatus exposed to the potentially explosive atmosphere but also other electrical apparatus with which it is interconnected is suitably constructed.
Inversion
In the air quality literature, the term inversion refers to a situation when the actual temperature gradient is positive (i.e., the temperature increases with height).
Inversion, Capping
A type of inversion that occurs aloft, at an elevation of about 1000 m, and marks the top of the layer of air subjected to strong vertical mixing during the day. The height of this layer is often referred to as the mixing depth, zi.
Inversion, Ground-Based
During calm and clear nights, the inversion can be as much as 100 or 200 m deep, causing inhibition of vertical growth of pollutant clouds.
Inversion, Synoptic
A persistent elevated inversion caused by subsiding air associated with a large-scale weather system such as a stagnant high pressure system.
Involuntary Risk
Risk that is imposed on someone who does not directly benefit from the activity that poses the risk.
Ionic Wind
In a corona discharge the inter-electrode space contains slow moving ions of a single polarity corresponding to the polarity of the sharp electrode. These make frequent collisions with neutral molecules of similar size to the ions resulting in momentum transfer and bulk gas movement in the direction of the electric field. The bulk gas movement, having a velocity of the order 1 m/s, is known as the ionic wind.
Ionization
The dissociation of air into ions by means of electrical energy.
IPL Response Time
The response time of an Independent Protection Layer.
Irritant
A substance which, by contact in sufficient concentration for a sufficient period of time, will cause an inflammatory response or reaction of the eye, skin, or respiratory system. The contact may be a single exposure or multiple exposures. Some primary irritant: chronic acid, nitric acid, sodium hydroxide, calcium chloride, amines, chlorinated hydrocarbons, ketones, alcohols. Importance: Knowing that a substance is an irritant allows you to be aware of the signs and symptoms of overexposure.
ISO 14000 / ISO 9000
Standards published by the International Organization for Standardization. ISO 14000 standards are for companies establishing an environmental management system. ISO 9000 standards are for companies establishing a quality management system.