Shallow-Layer Model with Terrain Effects
A dispersion model capable of predicting flows in variable terrain by using a simplification in the model formulation that makes the equations applicable only to a shallow layer of fluid.
Shelter-in-Place
A process for taking immediate shelter in a location readily accessible to the affected individual by sealing a single area (an example being a room) from outside contaminants and shutting off all HVAC systems.
Sheltering
Physical protection (such as an enclosed building) against the outcome of an incident.
Shock Absorber Device
See Detonation Momentum Attenuator.
Shock Sensitive
A relatively unstable material, the energetic decomposition of which can be initiated by merely the input of mechanical energy at normal ambient conditions. Materials are considered as shock sensitive if they are more easily initiated than dinitrobenzene in a standard drop-weight test.
Shock Wave
A transient change in the gas density, pressure, and velocity of the air surrounding an explosion point. The initial change can be either discontinuous or gradual. A discontinuous change is referred to as a shock wave, and a gradual change is known as a pressure wave.
Short Term Exposure Limit (STEL)
Is the limiting exposure concentration for exposure durations up to 15 minutes, as developed by the ACGIH.
Short-Stop Agent
A material added to a reaction mixture to stop or greatly reduce the reaction rate. This is usually done to prevent a runaway reaction.
Short-term Public Emergency Guidance Levels (SPEGLs)
For exposures whose occurrence is expected to be rare in the lifetime of any one individual, the 60-minute exposure concentration that reflects an acceptance of the statistical likelihood of a non-incapacitating reversible effect in an exposed population, while avoiding significant decrements in performance. Developed by the National Academy of Science (NAS).
Should
In this book the word "should" has been used to refer to action or guidance that is not mandatory. This has been applied to both the compliance and related audit criteria. The reason the compliance criteria are prefaced by should rather than shall, must, or other imperative terms is because the regulations described in this book that govern PSM programs from which the compliance criteria derived are performance-based in nature. Consequently, there may be multiple pathways to successful compliance and it is not the intent of this book to specify one method of compliance as being preferred or better than another, even inadvertently.
Shutdown (S/D)
A process by which an operating plant or system is brought to a safe and non-operating mode.
Side-On Pressure
The impulse or pressure experienced by an object as a blast wave passes by it.
Siemen (S)
Reciprocal ohm, formerly called a mho. See Conductivity.
Silicon Controlled Rectifier (SCR )
A semiconductor device that functions as an electrically controlled switch for DC loads. The SCR is one type of thyristor. A semiconductor device used to provide stepless control of an electric power circuit without the necessity of load matching; usually, two rectifiers are used in the circuit to provide full-wave control of the heater element, but in some instances two SCRs are used in a single package, known as a triac.
Similarity Model
A model of flow or dispersion where the key variables are scaled by similarity variables such as u*, L, or zo. The resulting scaled dimensionless variables may follow similarcurves and relationships.
Sink Mode Output
A mode of operation of solid state output devices in which the device controls the current from the load, i.e., when the output is energized it connects the load to the negative polarity of the supply.
Siting
The process of locating a complex, site, plant, or unit.
Six Sigma
A metric for measuring defects and improving quality. Also, a robust business improvement methodology that focuses an organization on customer requirements, process alignment, analytical rigor, and timely execution.
Skill Based Action
The performance of more or less subconscious routines governed by stored patterns of behavior. Examples might be the use of a hand tool by an experienced mechanic or the initiation of an emergency procedure by a trained and experienced operator.
Skill-Based Behavior
The performance of routine actions governed by stored patterns of behavior. Examples might be the use of a hand tool by an experienced mechanic or the initiation of an emergency procedure by a trained and experienced operator.
Skin
A notation, sometimes used with Permissable Eexposure Limit (PEL) or Threshold Limit Value (TLV) exposure date; indicates that the stated substance may be absorbed by the skin, mucous membranes, and eyes-either by airborne or direct contact-and that this additional exposure must be considered part of the total exposure to avoid exceeding the PEL or TLV for that substance. Even if workplace concentrations of a chemical do not exceed the TLV or PEL, the risk to health may be severe because breathing and skin contact are combined. Skin protection is advised.
Skin Friction Coefficient 2(u*/uref)2
The non-dimensional local surface shear stress coefficient. The engineering skin friction coefficient, cf, is traditionally tabulated in engineering texts. It is sometimes given as a function of surface type and ratio of roughness element height to pipe or boundary layer thickness. Often it is implicitly presented through the classic Moody diagram (Schlichting, 1955) which covers aerodynamically smooth and rough surfaces over a comprehensive range of Reynolds numbers including laminar, transitional, and turbulent flows
Skin Sensitizer
See "Sensitizer".
Skin Toxicity
See "Dermal Toxicity".
Slip Flange
Loose ring flange for connecting flared or stub end pipe. Continuity may be lost across connection due to insulation by nonconductive gasket plus painted surfaces on the slip flange and/or pipe. A conductive gasket (such as flexible graphite filled spiral wound metal type) or jumper cable may be required.
Smoldering
Flameless, oxygen diffusion limited combustion within either a porous char-forming material or a particulate bed.
Smoldering Nest
A small smoldering region within either a dust layer or a much larger quantity of particulate material.
So Far As Is Reasonably Practicable (SFAIRP)
A concept that is generally equivalent to As Low As Reasonably Practicable (however, there are some legal distinctions between the two terms in the UK).
Societal Risk
A measure of risk to a group of people. It is most often expressed in terms of the frequency distribution of multiple casualty events.
Software (S/W)
Programs, procedures, rules, and associated documentation required for the operating and/or maintenance of a digital system. Computer programs, routines, programming Languages and systems. The collection of related utility, assembly, and other programs that are desirable for properly presenting a given machine to a user. Including; detailed procedures to be followed, whether expressed as programs for a computer or as procedures for an operator or other person, documents, including hardware manuals and drawings, computer program listing, and diagrams, etc., and items such as those listed above, as contrasted with hardware.
Software Interlock
An interlock accomplished through an application program within a PES (see hard-wired interlock).
Softwired
See Software Interlock.
Solidity (ranges from 0 to 1)
Measure of lack of porosity of an object. For example, a solid building has a solidity of 1.0, while a pipe rack at a refinery has a solidity of 0.5.
Solubility in Water
A term expressing the percentage of a material (by weight) that will dissolve in water at ambient temperature. Importance: Solubility information can be useful in determining spill cleanup methods and fire-extinguishing agents and methods for a material.
Source Mode Output
A mode of operation of solid state output devices in which the device controls the current to the load (i.e., when the output is energized it connects the load to the positive polarity of the supply).
Source term
The release parameters (e.g. magnitude, rate, duration, orientation, temperature) that are the initial conditions for determining the consequences of the loss event for a hazardous material and/or energy release to the surroundings. For vapor dispersion modeling, it is the estimation, based on the release specification, of the actual cloud conditions of temperature, aerosol content, density, size, velocity and mass to be input into the dispersion model.
SOx
Oxides of Sulfur; undesirable air pollutants. Importance: Often listed on a MSDS as a hazardous decomposition product.
Spacing Table Approach
The use of established tables to determine minimum separation distances between equipment and buildings intended for occupancy. Industry groups, insurance associations, regulators and owner/operator companies have developed experience-based spacing tables for minimum building spacing for fire.
Sparging
Spraying; a sparger on a fermentor sprays air into the broth.
Spark Discharge
Transient discrete electric discharge which takes place between two conductors which are at different potentials, bridging the gap in the form of a single ionization channel.
Spark Extinguishing System
An extinguishing system in which the radiant energy of a spark or an ember is detected and the spark or ember is quenched.
Special Precautions
Instructions that describe proper handling and storage procedures specific to that material. Importance: Following these procedures would prevent excessive employee exposure. These procedures tell you additional information needed to handle the material safely.
Special Protection Information
A description of engineering precautions and personal protection that should be provided when working with a chemical in order to reduce an employee's exposure. Importance: Reducing the potential for exposure reduces the risk to health and safety.
Specific Gravity
A dimensionless, temperature dependent ratio of the density of one substance with that of a reference substance. For solids and liquids the reference substance is water at 39 F (4 C). For gases and vapors, the reference substance is dry air at 60 F (15.6 C).
Specific Impulse
The area under the overpressure versus time curve.
Specific Surface Area
The ratio of the particle surface area to the particle mass.
Spill or Leak Procedures
Steps that should be taken if a chemical spill or leak occurs. Importance: Proper removal of a chemical spill or leak from the work area eliminates the potential accumulation of hazardous concentrations of the chemical, reduces the risk of creating an environmental pollution problem and conforms to local, state and federal regulations.
Spill Prevention Control and Countermeasures Plan
The document prepared in compliance with U.S. regulation "Guidelines For The Preparation and Implementation of a Spill Prevention Control and Countermeasure Plan (SPCC)" (EPA 40 CFR part 112.7. 216)
Spinning Riffler
A device for obtaining a representative sample of particulate material from a large bag or container.
Spontaneous Combustion (Heating) of Powders
Ignition of powders in bulk caused by the rate of heat generation from oxidation and/or exothermic decomposition reactions of the powders being greater than the rate of heat loss to the surroundings.