Bow Tie Model
A risk diagram showing how various threats can lead to a loss of control of a hazard and allow this unsafe condition to develop into a number of undesired consequences. The diagram can also show all the barriers and degradation controls deployed.
Branch point
A node with two paths in an event tree or cause-consequence diagram. One path represents success of a safeguard and the other path represents failure of the safeguard.
Breakdown Strength
The minimum voltage for spark breakdown to occur across a material of given thickness held between electrodes producing a uniform electric field under specified test conditions. Expressed as volts per unit thickness. As the potential across any material is increased, Ohm's law is typically obeyed initially, followed by a region of non-Ohmic behavior; finally a potential is reached at which the current increases at an uncontrolled rate. The corresponding field is the breakdown strength, also known as breakdown field, dielectric strength, and electric strength. Insulator breakdown strengths are typically 106 to 109 V/m at room temperature, varying considerably with test method. High vacuum has the highest breakdown strength followed by thin homogeneous solids and then liquids.
Breakdown Voltage
The minimum voltage for spark breakdown of a specified gas mixture between electrodes producing a uniform electric field, for specified values of the product of gas density and gap length.
Broth (fermentation/cell culture)
the cells, nutrients, waste, and other components that make up the contents of a microbial bioreactor.
Brownfield
An industrial or commercial property that is abandoned or underused and being considered as a potential site for redevelopment.
Brush Discharge
A higher energy form of corona discharge characterized by low frequency bursts or streamers. The simplest type forms between charged, isolated nonconductive surfaces and grounded conductors acting as electrodes. For positive electrode, pre-onset or breakdown streamers are observed and the maximum effective energy is 5 - 10 mJ,while for negative electrode the maximum effective energy is a few tenths of a mJ. Brush discharges may ignite flammable gas and hybrid mixtures but not dust in air. Brush discharges may also form on nonconductive layers with grounded substrates. These include transitional brush discharges which have a greater effective energy than brushes from isolated nonconductors but a smaller effective energy than propagating brushes.
Brush Discharge
A higher energy form of corona discharge characterized by low frequency bursts or streamers. The simplest type forms between charged, isolated nonconductive surfaces and grounded conductors acting as electrodes.
Building
A rigid, enclosed structure.
Building Downwash Models
Models used for estimating the flow and dispersion in and near the recirculating cavity behind buildings, where plumes may downwash to the ground.
Building Geographic Risk
The risk to a person who occupies a specific building 24 hours/day, 365 days/year.
Building Siting Evaluation
The procedures used to evaluate the hazards and establish the design criteria for new buildings and the suitability of existing buildings at their specific locations.
Bulking Brush Discharge
A partial surface discharge created during bulking of powder in containers, appearing as a luminous, branched channel flashing radially from the wall toward the center of the container. Its maximum effective energy with respect to dust ignition is believed to be 10 - 20 mJ (less than the MIE of Lycopodium). May ignite flammable gas, hybrid mixtures and some fine dusts in air. Owing to large size of phenomenon the effective energy cannot be measured directly but instead must be inferred from accident case histories where dust of known spark MIE was ignited with proper grounding in place.
Buoyant Cloud
The in-cloud density is less than the ambient density, due to the emissions of hot gases or materials with low molecular weight. Buoyant cloud and light cloud are synonymous.
Buoyant Force
Mathematically, (rcld - rair)gVcld (in Newtons), the product of the difference in density of a cloud and the surrounding medium (air), the gravitational acceleration, and the volume of the cloud.
Buoyant Gas
See Positively Buoyant Gas.
Buoyant turbulence
Generated by heating of the ground surface by the sun and is suppressed by cooling of the ground surface at night. Surface heating leads to the formation of buoyant thermal bubbles from the warm ground surface on sunny afternoons. The opposite effect happens during clear nights, when the surface cooling causes the suppression of turbulence.
Burnback Resistance
The ability of a flame arrester to maintain its mechanical integrity and prevent flame breakthrough when the flame arrester is subjected to a standing flame. See also Endurance Burn(ing).
Burning Velocity
Burning velocity is the speed at which a flame front propagates relative to the unburned gas. This differs from flame speed. The laminar burning velocity (SL) is the speed at which a laminar (planar) combustion wave propagates relative to the unburned gas mixture ahead of it. The fundamental burning velocity (Su) is similar, but generally not identical to, the observed laminar burning velocity. This is because Su is a characteristic parameter referring to standardized unburned gas conditions (normally 760 mm Hg and 25 degrees C), and which has been corrected for nonidealities in the measurement. The turbulent burning velocity (St) exceeds the burning velocity measured under laminar conditions to a degree depending on the scale and intensity of turbulence in the unburned gas.
Bus
One or more conductors used for transmitting signals or power from one or more sources to one or more destinations.
By Exception
A form of documentation where only information that fits a certain definition is documented and not all of the information that was generated by the activity. For example, in a HIRA, this most commonly happens when only those hazard scenarios that resulted in a recommendation(s) are documented and no others. In Asset Integrity, only those ITPM tasks that result in an out-of-specification result are documented.
Byte
A data element of length 8 bits.
C or Ceiling
The letter "C" or the word "ceiling" on the TLV or PEL shows the highest airborne concentration of a specific chemical that is allowed in the workplace. This concentration should never be exceeded, even for short periods of time. See also, "PEL" and "TLV". Importance: Chemicals that react rapidly in the body, causing ill health effects carry this value.
Calculated Adiabatic Reaction Temperature (CART)
See Flame Temperature
Calendar Time
The period between starting date and ending date.
Canvey Island Study
An early (1978) quantitative risk assessment which evaluated the risks associated with an integrated chemical/petrochemical processing complex in the UK.
Capability
When assessing the capability of an adversary, two distinct capabilities need to be considered. The first is the capability to obtain, damage, or destroy the asset. The second is the adversary's capability to use the asset to achieve its objectives once the asset is obtained, damaged, or destroyed.
Capability Assessment
A systematic review of a system's ability to perform to meet system requirements under abnormal and perturbed dynamic conditions.
Capacitance (C).
The constant of proportionality between charge and potential difference for systems of conductive bodies. The capacitance in Farads is the charge in Coulombs which must be communicated to raise the potential difference by 1.
Car Seal
A metal or plastic cable used to fix a valve in the open position (car seal open) or closed position (car seal closed). Proper authorization, controlled via administrative procedures, must be obtained before operating the valve. The physical seal should have suitable mechanical strength to prevent unauthorized valve operation.
Carcinogen
A material that has been found by the International Agency for Research on Cancer or the National Toxicology Program to produce or potentially produce some type of cancer
Carr Indices
Measures of particulate physical properties (such as bulk density) based on standard test methods.
CAS Registry Number
A unique number having up to nine digits that is assigned to a chemical by the Chemical Abstracts Service of the American Chemical Society. With the exception of aqueous solutions, mixtures are not covered under this registry.
Cascade Impactor
Device used to collect and segregate particles by their aerodynamic diameters.
Cascading
See Pressure Piling
Catalogued Device
A device that is listed in the manufacturer's catalogue of PES components.
Catalyst
A chemical substance that accelerates the rate of a chemical reaction by lowering the energy of activation required for the chemical reaction to occur.
Catastrophic
A loss with major consequences and unacceptable lasting effects, usually involving significant harm to humans, substantial damage to the environment, and/or loss of community trust with possible loss of franchise to operate.
Catastrophic Failure
A failure which is both sudden and causes termination of one or more fundamental functions.
Catastrophic Incident
An incident involving a major uncontrolled emission, fire or explosion that causes significant damage, injuries and/or fatalities onsite and have an outcome effect zone that extends into the surrounding community.
Catastrophic Release
An uncontrolled loss of containment of toxic, reactive, or flammable materials from a process that has the potential for causing onsite or offsite acute health effects, significant environmental effects (e.g., compromise of a public drinking water supply), or significant on-site or off-site property damage.
Catch Tank
A separate containment vessel intended to receive an emergency discharge from relief devices in the process vessel's vapor space. Catch tanks are usually employed where substantial two-phase relief flow, entrained solids, or reaction mass carryover is expected to occur.
Category M
A fluid service in which the potential for personnel exposure is judged to be significant, and in which a single exposure to a very small quantity of a toxic fluid, caused by leakage, can produce serious irreversible harm to persons upon breathing or bodily contact, even when prompt restorative measures are taken (ASME B31.3).
Causal factor (CF)
A major unplanned, unintended contributor to an incident (a negative event or undesirable condition), that if eliminated would have either prevented the occurrence of the incident or reduced its severity or frequency. Also known as a critical causal factor or contributing cause.
Causal factor chart
A sequence diagram that graphically depicts an incident from beginning to end; typically used to organize incident data and identify causal factors.
Cause (in Hazard Evaluation)
In the context of hazard evaluation procedures, an initiating cause.
Cause (Incident)
An event, situation, or condition which results, or could result (Potential Cause), directly or indirectly in an accident or incident.
Cause-Consequence Analysis [Cause-Consequence Diagrams]
A method for illustrating the possible outcomes arising from the logical combination of selected input events or states. A combination of Fault Tree and Event Tree models.
Cell (in study cube)
One of the 27 different categories of CPQRA, defined by a unique value for each axis of the study cube.
Centerline height
Elevation of plume centerline above ground after plume rise is completed.