Dispersion Coefficients
σ y (lateral component), σ z (vertical component), and σ x (along-wind component)
Dispersion Modeling
A technique that can be used to confirm that the residual or converted products from a normally operating end-of-pipe treatment system do not present any residual hazards to plant personnel, community, or environment. In addition, modeling could be employed to assess the impact on plant personnel, community, or environment if the treatment system malfunctions and releases the collected vent streams untreated.
Dispersion Models
Mathematical models that characterize the transport of toxic/flammable materials released to the air and/or the water.
Displacement Length , d
A scaling length that becomes important for describing the wind profile at elevations close to the average roughness obstacle height, Hr, for densely packed roughness obstacles. It describes the vertical displacement (from the ground surface) of the effective ground level and is approximately equal to 0.5 Hr for obstacle types such as urban centers, tall crops, and forests.
Displacement zones
Recirculation zones adjacent to buildings or other obstacles where the flow has separated from the obstacle and reattached downwind.
Disproportionation
A chemical reaction in which a single compound serves as both oxidizing and reducing agent and is thereby converted into a more oxidized and a more reduced derivative; e.g., a hypochlorite upon appropriate heating yields a chlorate and a chloride.
Dissipation
See Effective Conductivity.
Distributed Control System (DCS)
A system which divides process control functions into specific areas interconnected by communications (normally data highways), to form a single entity. It is characterized by digital controllers and typically by central operation interfaces. Distributed control systems consist of subsystems that are functionally integrated but may be physically separated and remotely located from one another. Distributed control systems generally have at least one shared function within the system. This may be the controller, the communication link or the display device. All three of these functions maybe shared. A system of dividing plant or process control into several areas of responsibility, each managed by its own CPU, with the whole interconnected to form a single entity usually by communication buses of various kinds.
Diversity
The performance of the same overall protective function by a number of independent and different means.
DNA vaccine (nucleic acid vaccine)
Injection of a gene that codes for a specific antigen, enabling the recipient to produce that antigen directly to achieve the desired immune response.
Domino Effects
The triggering of secondary events, such as toxic releases, by a primary event, such as an explosion, such that the result is an increase in consequences or area of an effect zone. Generally only considered when a significant escalation of the original incident results.
Dose
Time-integrated concentration
Dow Chemical Exposure Index (CEI)
A method, developed by The Dow Chemical Company, used to identify and rank the relative acute health hazards associated with potential chemical releases. The CEI is calculated from five factors: a measure of toxicity; the quantity of volatile material available for a release; the distance to each area of concern; the molecular weight of the material being evaluated; and process variables that can affect the conditions of a release such as temperature, pressure, and reactivity.
Dow Fire and Explosion Index (F&EI)
A method (developed by Dow Chemical Company) for ranking the relative fire and explosion risk associated with a process. Analysts calculate various hazard and explosion indexes using material characteristics and process data.
Drag Force
The surface stress, to, arises through direct viscous stress and through the pressure asymmetry around roughness elements on the surface (sometimes called form or pressure drag). In atmospheric flows the pressure asymmetry dominates over direct viscous stresses and it produces a drag force, commonly called the drag, on the roughness elements.
Dry Adiabatic Lapse Rate (DALR)
The negative of the temperature gradient established as dry air ascending in the atmosphere. For air with a molecular weight of 29 and a specific heat ratio of 1.41 the DALR = 0.995 degC/100m.
Dry Deposition
Effective downward vertical velocity of small aerosols and gases if they are chemically reactive with the ground surface. In many cases, this process is a function of the ability of a vegetative leaf to absorb the substance once the substance passes through the openings in the leaf surface. For most materials, a dry deposition velocity of about 0.01 m/s can be assumed.
Dry Type Flame Arrester
A flame arrester that uses an element consisting of small gaps or apertures to quench and extinguish the flame, as distinguished from hydraulic flame arresters.
Dtex
Fiber weight per unit length (gram/10-km length)
Dump Tank
A separate collection and containment vessel intended to receive an emergency discharge of liquids, liquid reaction mass, or slurries originating from the bottom of a process vessel or reactor. The dump is usually automatically triggered by a process safety interlock, but may also be initiated manually. An uncontrolled exothermic or other runaway reaction can be controlled by discharging the process vessel contents to the dump tank. This may allow the process vessel to be returned to service in a shorter time.
Duration
The length of time for which the event state exists. Can be the repair time. Dimension (Time). The amount of time taken by an event or action.
Dust
Any finely divided solid, 420 microns or 0.017 inches, or less in diameter (that is, material that can pass through a U.S. No. 40 standard sieve).
Dust Hazard Analysis (DHA)
A systematic review to identify and evaluate the potential fire, flash fire, or explosion hazards associated with the presence of one or more combustible particulate solids in a process or facility.
Dynamic Testing
Consists of processor routines in conjunction with external hardware under PLC control. General guidelines for dynamic testing of critical inputs and outputs are described below: Critical Inputs Procedure - Disconnect inputs to Module A. Check for zero on all inputs.If test fails, disable inputs and generate alarm. If test succeeds, reconnect inputs and repeat for Module B. PES Files: Store results of tests. Critical Outputs Procedure - Check that Module B is energized. If B is enabled, disable Module A. Check that A outputs are de-energized (through feedback via input module). If test fails, disable outputs and generate alarm. If test succeeds, reenergize outputs and repeat for Module B. PES Files: Store results of tests.
Edible vaccines
Plants or vegetables (such as potato) that are engineered to express an antigenic protein. Upon consumption, the protein is recognized by the immune system and vaccinates the patient against the original antigen.
Effect Models
Models that predict effects of incident outcomes usually with respect to human injury or fatality or property damage.
Effect Zone
For an incident that produces an incident outcome of toxic release, the area over which the airborne concentration equals or exceeds some level of concern. For a flammable release, the area over which a particular incident outcome case produces an effect based on a specified criterion. For a loss of containment incident producing thermal effects, the area over which a particular incident outcome case produces an effect based on a specified radiative heat stress limit.
Effective Conductivity
The charging process in liquids of low conductivity alters the concentration of charge carriers. In the charged state, such as downstream of microfilters, petroleum products with measured (rest) conductivities above about 2 pS/m often display a relaxation time a factor of 3-4 times longer than predicted. However, for rest conductivities less than about 2 pS/m, relaxation times become much shorter than predicted. For example, the relaxation time of jet fuel having a conductivity of 0.01 pS/m is about 30 min based on Ohmic relaxation. In practice it is found that highly charged, non-viscous liquids of such low conductivity relax charge hyperbolically rather than Ohmically. The provision of 100 s of residence time downstream of filters is found to reduce the charge to about 5% of its initial value, whereas via Ohmic relaxation this would require three relaxation times (>1 hour) of residence time. In Appendix B, non-viscous liquids whose rest conductivities are usually measured at about 2 pS/m or less are not assigned a relaxation time but instead a 100 s dissipation time.
Effective Energy of Static Discharge
The spark ignition energy (J) of the least easily ignitable flammable mixture known to have been ignited by the static discharge.
Effective Transport Speed, ue
Defined as the vertical integral of the concentration-weighted wind speed, uc = ? u(z)C(z) dz / ? C(z) dz, where z is the height above ground, C(z) is the height-variable concentration of pollutant in the cloud, and u(z) is the height-variable wind speed. ue is also known as the cloud advective speed.
Effectiveness
The combination of process safety management performance and process safety management efficiency. An effective process safety management program produces the required work products of sufficient quality while consuming the minimum amount of resources.
Efficacy
The proven ability of a drug or vaccine to produce a desired clinical effect at the optimal dose.
Electric Field Intensity (E).
A measure of the force exerted by one charged body on another. Imaginary lines of force or electric field lines originate (by convention) on positive charges and terminate on negative charges. They can be thought of as elastic lines which repel each other in a direction perpendicular to the line itself. The electric field intensity (volts/meter) at any location is the force (Newtons) that would be experienced by unit test charge (Coulombs) placed at the location. A uniform electric field is an ideal case in which the electric field lines are parallel with one another, for example between the plates of a large, parallel plate air capacitor. A divergent electric field is one in which the field intensity changes with distance, for example in a capacitor comprising a sphere and a plate. In practical situations electric fields are rarely uniform, particularly within solids and liquids.
Electromagnetic Interference
Electromagnetic phenomena which, either directly or indirectly, can contribute to degradation in performance of an electronic receiver or system. (The terms Radio Interference, Radio-Frequency Interference (RFI), noise, and EMI have been employed at various times in the same context).
Electromagnetic Interference (EMI)
Any spurious effect produced in the circuits or elements of a device by external electromagnetic fields.
Electromagnetic Pulse (EMP)
A reaction of large magnitude resulting from the detonation of nuclear weapons. A type of disturbance that leads to noise in radio-frequency electric or electronic circuits. A pulse of electromagnetic radiation generated by a large thermonuclear explosion.
Electrophoresis
The phenomenon of particle migration in an electric field.
Electrophorus
An early device for generating charge by induction, attributed to and named in 1775 by Volta. Comprises a nonconductive plate or cake which can be charged by rubbing, and an isolated metal plate which can be placed on the charged cake. After contact is made, a charge is induced on the metal plate; if the top of the metal plate is grounded momentarily, the like charge induced by the cake is conducted to ground while an equal and opposite charge remains on the metal plate. After the plate is lifted from the cake, it retains the opposite charge. The process may be repeated indefinitely to produce charge on metal plates without recharging the cake. Charge transfers are typically of the order 1 mC.
Element
Basic division in a process safety management system that correlates to the type of work that must be done (e.g., management of change [MOC]).
Element (Software)
The portion of a graphical Language corresponding to an Instruction in Textual Language. The Operation Part and the Operand Part as specified by appropriate combination of graphic and character symbols.
Element Owner
the person charged with overall responsibility for overseeing a particular RBPS element. This role is normally assigned to someone who has management or technical oversight of the bulk of the work activities associated with the element, not necessarily someone who performs the work activities on a day-to-day basis.
Elevated clouds or plumes
Pollutant releases at elevations above about 10 or 20 m.
Emergency and First Aid Procedures
Actions that should be taken at the time of a chemical exposure before trained medical personnel arrive. Importance: These procedures may lessen the severity of an injury or save a person's life if done immediately following a chemical exposure.
Emergency Exposure Guideline Limits (EEPG)
Maximum concentration levels that provide guidance in advance planning for management of emergencies. Developed by the National Academy of Sciences (NAS).
Emergency Management
A PSM program element involving work activities to plan for and respond to emergencies.
Emergency Operations
Process changes initiated by the operations staff to place the process into a safe condition (back to normal operations or shutdown) in response to any abnormal situation that could cause a release, explosion, or other significant event.
Emergency Relief Device
A device that is designed to open during emergency or abnormal conditions to prevent rise of internal fluid pressure in excess of a specified value. The device also may be designed to prevent excessive internal vacuum. The device may be a pressure relief valve, a non-reclosing pressure relief device, or a vacuum relief valve.
Emergency Response Plan
A written plan which addresses actions to take in case of plant fire, explosion or accidental chemical release.
Emergency Response Planning Guidelines (ERPG)
A system of guidelines for airborne concentrations of toxic materials prepared by the AIHA. For example, ERPG-2 is the maximum airborne concentration below which it is believed nearly all individuals could be exposed for up to one hour without experiencing or developing irreversible or other serious health effects or symptoms that could impair an individual's ability to take protective action.
Emergency Sequence
An automatic sequence initiated by an interlock. The sequence may consist of starting, stopping, opening, or closing equipment in order to render the process safe.