Hazard
An inherent chemical or physical characteristic that has the potential for causing damage to people, property, or the environment.
Hazard Analysis
The identification of undesired events that lead to the materialization of a hazard, the analysis of the mechanisms by which these undesired events could occur and usually the estimation of the consequences.
Hazard and Operability Study (HAZOP)
A systematic qualitative technique to identify process hazards and potential operating problems using a series of guide words to study process deviations. A HAZOP is used to question every part of a process to discover what deviations from the intention of the design can occur and what their causes and consequences may be. This is done systematically by applying suitable guidewords. This is a systematic detailed review technique, for both batch and continuous plants, which can be applied to new or existing processes to identify hazards.
Hazard Checklist
An experience-based list of hazards, potential incident situations, or other process safety concerns used to stimulate the identification of hazardous situations for a process or operation.
Hazard Classifications
Broken into three categories, "Safety and Environmental", "High Business Risk", and "Low Business Risk."
Hazard Evaluation
Identification of individual hazards of a system, determination of the mechanisms by which they could give rise to undesired events, and evaluation of the consequences of these events on health (including public health), environment and property. Uses qualitative techniques to pinpoint weaknesses in the design and operation of facilities that could lead to incidents.
Hazard Frequency of Potential Hazards
(i.e., Demand Rate) times the Fractional Deadtime of Safety Systems describes the relationship between hazard rate and demand rate.
Hazard Identification
Part of the Hazards Identification and Risk Analysis (HIRA) method in which the material and energy hazards of the process, along with the siting and layout of the facility, are identified so that a risk analysis can be performed on potential incident scenarios.
Hazard Identification and Risk Analysis (HIRA)
A collective term that encompasses all activities involved in identifying hazards and evaluating risk at facilities, throughout their life cycle, to make certain that risks to employees, the public, or the environment are consistently controlled within the organization's risk tolerance.
Hazard Rate
The frequency with which hazards occur. Dimension (Time -1). The frequency at which failures lead to hazardous events. Also known as the Time-Related Equipment Failure Rate, is an Instantaneous Failure Rate function of time.
Hazard Warning Structure
A modified form of fault tree highlighting event mitigating feature pairs. These are often pairings of incident precursors and protective devices or event terminating features which are combined through an AND gate.
Hazard Zone
For an incident that produces an outcome such as toxic release, the hazard zone is the area over which the airborne concentration equals or exceeds some level of concern. For a flammable release, the area of effect is based on a specified level of thermal radiation. For a release that results in explosion, this is the area defined by specified overpressure levels.
Hazardous Chemical
A material that is toxic, reactive, or flammable and is capable of causing a process safety incident if released. Also Hazardous material.
Hazardous Chemical Reactivity
Any chemical reaction with the potential to exhibit rates of increase in temperature and/or pressure too high to be absorbed by the environment surrounding the system. Included are reactive materials and unstable materials.
Hazardous Energy Control Procedure
Written procedure for affixing appropriate lockout devices or tag out devices to energy isolating devices, and to otherwise disable machines or equipment to prevent unexpected energization, start up or release of stored energy in order to prevent injury to employees.
Hazardous Event
See Loss event.
Hazardous Material
In a broad sense, any substance or mixture of substances having properties capable of producing adverse effects to the health or safety of human beings or the environment. Material presenting dangers beyond the fire problems relating to flash point and boiling point. These dangers may arise from, but are not limited to, toxicity, reactivity, instability, or corrosivity
Hazardous Particulate Solids
In a broad sense, any particulate solids or mixture of particulate solids having properties capable of producing adverse effects to the health or safety of process equipment, human beings, or the environment. These can include such properties as combustibility, flammability, explosibility, toxicity, corrosiveness, etc.
Hazardous Waste (40 CFR 261)
Hazardous waste can be classified as follows: Ignitable: Based upon the flash point of a liquid waste; for a solid, the capability to cause fire through friction or absorption of moisture, and to burn vigorously and persistently; solids that meet the 49 CFR definition of oxidizer; and, compressed gases that are ignitable under the DOT definition. Corrosive: Liquid wastes that have a pH of plain 2 or 12.5, or that corrode steel at a rate of greater than 0.25 inch per year. Reactive: Wastes that are unstable and readily undergo violent change; that react violently with water or when mixed with water generate toxic vapors or fumes; that are cyanide or sulfide bearing and can generate toxic gases, vapors, or fumes at pH conditions between 2 and 12.5; that are readily capable of detonation or explosion at standard temperature and pressure if subjected to a strong initiating force or if heated under confinement; or DOT forbidden explosives. Toxic: Liquid wastes or extract from waste solids that fail the Toxicity Characteristic Leaching Procedure (TCLP) analytical test because they contain certain designated metals, pesticides, or organic chemicals at concentrations equal to or, in excess of, specified regulatory limits.
HAZOP/LOPA Study
The extension of a HAZOP Study to include aspects of a LOPA, including selecting identified scenarios for further analysis; evaluating the initiating event frequency, consequence severity and effectiveness of IPLs on an order-of-magnitude basis; considering enabling conditions and/or conditional modifiers as appropriate when evaluating scenario risk; and comparing the calculated scenario risk to a risk goal to determine the adequacy of existing risk control measures.
Health Hazard
A chemical for which there is statistically significant evidence based on at least one study conducted in accordance with established scientific principles that acute or chronic health effects may occur in exposed employees. (OSHA 1994)
Heat
Sufficient energy must be applied to raise the fuel to its ignition temperature.
Heat of Combustion, Hci
The heat of reaction obtained by burning a unit mass of
Heat of Reaction
The net difference in heat of formation of all reactants and of all products in an adiabatic system. The reaction is exothermic if heat is released (heat of reaction is negative), and endothermic if heat is absorbed by the reaction.
Heavy Gas
A gas with density exceeding that of air at ambient temperature. See also dense gas and negatively buoyant vapors.
Hexadecimal
Pertaining to the numeration system with a radix of sixteen.
High Potential Incident
An event that, under different circumstances, might easily have resulted in a catastrophic loss
High Velocity Vent Valve
A device to prevent the passage of flame in the reverse direction, consisting of a mechanical valve which adjusts the opening available for flow in accordance with the pressure at the inlet of the valve in such a way that the efflux (exiting) velocity cannot be less than 30 m/s.
Highly Hazardous chemical
A material that is toxic, reactive, or flammable and is capable of causing a process safety incident if released. These materials are included in OSHA's PSM Standard, 29 CFR 1910.119.
Historical Data
Data recorded from actual past experience.
Historical Error
Actions by designers, operators, or managers that may contribute to or result in accidents.
Historical Incident Data
Data collected and recorded from past incidents.
Host Cell
a cell whose metabolism is used by a virus for growth and reproduction or into which a plasmid is introduced in recombinant DNA experiments; in bioprocessing, the cells engineered and cultured to express a protein of interest are the expression system host cells.
Host Factor
The intrinsic factor such as age, race, sex, or behavior that influences a person's exposure, susceptibility, or response to a causative agent.
Hot Work
Any operation that uses flames or can produce sparks (e.g., welding).
Hot-flame Ignition
A rapid, self-sustaining, sometimes audible gas phase reaction of the sample or its decomposition products with an oxidant. A readily visible yellow or blue flame usually accompanies the reaction. (NFPA 325 2001)
HRA Event Tree
A graphical representation of sequential events in which the tree limbs designate human actions and other events as well as different conditions or influences upon these events. The values assigned to all tree limbs (except those in the first branching) are conditional probabilities. At any branch point in the tree, the sum of the probability values assigned to all of the limbs emanating from that point is 1.0. Typically the HRA event tree is drawn as a binary tree (i.e., only two limbs at each branch point).
HSE Risk Interval
A single-value measure of societal risk that can be calculated from the data used to develop an F-N curve, or can be estimated based upon an assumed shape for the F-N curve and information on a proposed "worst case" scenario.
Human Error
Intended or unintended human action or inaction that produces an inappropriate result. Includes actions by designers, operators, engineers, or managers that may contribute to or result in accidents.
Human Error Probability
The ratio between the number of human errors and the number of opportunities for human error. Synonyms: human failure probability and task failure probability.
Human Factors
A discipline concerned with designing machines, operations, and work environments so that they match human capabilities, limitations, and needs. Includes any technical work (engineering, procedure writing, worker training, worker selection, etc.) related to the human factor in operator-machine systems.
Human Performance Technology
A systematic approach to improving productivity and competence that uses a set of methods and procedures to realize opportunities related to the performance of people.
Human Reliability Analysis (HRA)
A method used to evaluate whether system-required human-actions, tasks, or jobs will be completed successfully within a required time period. Also used to determine the probability that no extraneous human actions detrimental to the system will be performed.
Hybrid Mixture
A mixture of a flammable gas with either a combustible dust or combustible mist.
Hydration
The incorporation of molecular water into a complex molecule with the molecules or units of another species. The complex may be held together by relatively weak forces or may exist as a definite compound. Parker 1997
Hydraulic Diameter
An equivalent diameter for noncircular apertures which is equal to 4x(aperture area/aperture perimeter).
Hydraulic Flame Arrester
A flame arrester consisting of a vessel filled with a seal fluid (often water) and a distributor which breaks up the incoming gas into discrete bubbles, thus facilitating quenching of the flame and preventing flame transmission.
Hypergolic
Hypergolic behavior is characterized by immediate, spontaneous ignition of an oxidation reaction upon mixing of two or more substances.
Hypothetical Individual
A modeling construct that allows the risk estimate to reflect variations in exposure durations or patterns, diverse forms of protection available to different population groups, variations in individual characteristics that might affect susceptibility to harm (e.g., age, gender, abilities or disabilities), and so forth. Multiple risk calculations may be required to determine the hypothetical individual at greatest risk at a particular location.
Identification and Prioritization
Consists of (1) cataloging the hazardous materials and modes of transportation, (2) identifying sensitive areas and potential points of failure along the transit route, and (3) understanding interactions with other stakeholders in the supply chain. This process enables the identification of shipments that may require special attention, including escalating issues/scenarios for more detailed risk analysis.