Safeguard
Any device, system, or action that interrupts the chain of events following an initiating event or that mitigates the consequences.
Safety
The expectation that a system does not, under defined conditions, lead to a state in which human life, economics or environment are endangered.
Safety Instrumented Functions (SIF)
A system composed of servers, logic servers, and final control elements for the purpose of taking the process to a safe state when predetermined conditions are violated.
Safety Instrumented System (SIS)
A separate and independent combination of sensors, logic solvers, final elements, and support systems that are designed and managed to achieve a specified safety integrity level. A SIS may implement one or more Safety Instrumented Functions (SIFs).
Safety Integrity
(there is no definition for this CPQRA) is defined as the likelihood that a safety-related system will achieve its required safety functions under all the stated conditions within a specified period of time.
Safety integrity level (SIL)
Discrete level (one out of four) allocated to the SIF for specifying the safety integrity requirements to be achieved by the SIS.
Safety Interlocking
Same as interlocking except a failure to control out-of-limit conditions can cause injury or unacceptable environmental contamination.
Safety Layer
A system or subsystem that is considered adequate to protect against a specific hazard. The safety layer; Cannot be compromised by the failure of another safety layer, is totally independent of any other protective layers, may be a non-control alternative (e.g., chemical, mechanical), may be an administrative procedure, may require diverse hardware and software packages, must be approved according to company policy and procedures, must have acceptable reliability, and must meet proper equipment classification.
Safety Review
An inspection of a plant or process unit, drawings, procedures, emergency plans, and/or management systems, etc., usually by a team and usually problem-solving in nature. (See Audit for contrast.)
Safety System
Equipment and/or procedures designed to limit or terminate an incident sequence, thus avoiding a loss event or mitigating its consequences.
Sampling
Selecting a portion of a large population of data or information to determine the accuracy, representativeness, or characteristics of the entire population.
Sampling Time
The length of time in atmospheric dispersion testing over which concentration data are sampled. Sampling time is normally synonymous with averaging time.
Satellite Instrument House (SIH)
A structure containing instrument and process control equipment for one or more process units
Sauter Mean Diameter
The ratio of the cube of the volume mean diameter to the square of the surface mean diameter; roughly the ratio of the particle volume to its surface area.
SBR
Semi-Batch Reactor; A type of batch reactor that is characterized by the supply of a key reactant to the reactor during the reaction. Products are only taken from the reactor upon conclusion of the reaction process. Both heat generation and concentrations in the batch reactor vary during the reaction process.
Scale-up
The steps involved in transferring a manufacturing process or section of a process from laboratory scale to the level of commercial production.
Scaling
Adjusting the relative size of a risk criterion, at a given level in the enterprise, based upon factors such as scale of operation. For example, the societal risk criterion for a business sector might be apportioned to the various sites within the sector with sites receiving differing shares of the allotment. Scaling is not applicable to individual risk.
Scan Time
See Time.
Scenario
A detailed description of an unplanned event or incident sequence that results in a loss event and its associated impacts, including the success or failure of safeguards involved in the incident sequence.
Screening Tool
A simplified dispersion model with limited capabilities, suitable for screening-level studies.
Scribe/recorder
A hazard evaluation team member who is responsible for capturing the significant results of discussions that occur during a hazard evaluation team meeting.
Security
A password, key, procedure, or other device which has the ability to limit change in selected parameters. The existence and enforcement of techniques which restrict access to data, and the conditions under which data may be obtained.
Security Plan
A document that describes a plan to address security issues and related events including security assessment and mitigation options. This includes security alert levels and response measures to security threats.
Security Risk
The potential for damage to, or loss of, an asset. Risk, in the context of chemical process security, is the potential for the intentional event outcome to be realized. Typical examples include an intentional release of hazardous materials from containment, the theft of chemicals that could later be used as weapons, the contamination of chemicals that may later harm the public, the economic costs of the damage, or disruption of the chemical process or other nearby critical infrastructure. Therefore, risk is an expression of the likelihood (LAS) that a specific vulnerability (V) of a particular attractive target (AT) will be exploited by a defined threat (T) to cause a given consequence (C).
Security Vulnerability Analysis (SVA)
The process of determining the likelihood of an adversary successfully exploiting a weakness and the resulting degree of damage or impact. A SVA is not a quantitative risk analysis, but is performed qualitatively using a structured and repeatable method and the best judgment of safety, security, and transportation personnel. A qualitative determination of risk is the desired outcome of a SVA in order to provide the basis for ranking the security-related risks and thus to establish priorities for the application of countermeasures.
Select Agents
Organisms that are of particular concern to the federal government because of their potential use as biological weapons.
Selectivity
The selectivity (ap) is the ratio of the amount of a desired product P obtained and the amount of a key reactant converted.
Self-Accelerating Decomposition Temperature (SADT)
The lowest temperature that a mass of material, capable of an exothermic decomposition reaction, must be held such that the heat of decomposition exceeds the amount of energy lost to the surroundings. This will result in an increase in the mass temperature and acceleration of the decomposition reaction rate.
Self-Heating of Powders
See Spontaneous Combustion (Heating) of Powders.
Self-Igniting
The ignition and sustained combustion of a substance without introduction of any ignition source besides thermal energy or heat of reaction resulting when combined with other substances in the surrounding environment. Self-igniting materials include materials above their autoignition temperature, chemicals that ignite due to heat of reaction with oxygen in air, and chemicals that are unstable and spontaneously combust when released.
Self-reactive
Capable of polymerization, decomposition or rearrangement. Initiation of the reaction can be spontaneous, by energy input such as thermal or mechanical energy, or by catalytic action increasing the reaction rate.
Semi-Batch Reactor
A reactor in which some reactants are added to the reactor at the start of the batch, while others are fed intermittently or continuously during the course of the reaction.
Semi-Batch Reactor
In a semi-batch reactor, some reactants are added to the reactor at the start of the batch, while others are fed continuously during the course of the reaction.
Semi-Quantitative
Risk analysis methodology that includes some degree of quantification of consequence, likelihood, and/or risk level.
Semi-Quantitative Risk Analysis
Risk analysis methodology that includes some degree of quantification of consequence, likelihood, and/or risk level.
Semiconductive
Possessing a conductivity between 102 and 104 pS/m or a resistivity between 108 and 1010 W-m.
Semiconductive Hose
Having an electrical resistance great enough to limit the flow of stray electric current to safe levels, yet not so great as to prevent relaxation of static electrical charges to ground. Typically achieved using carbon-loaded layers yielding 103 to 105 ohm/m of hose length. In a flammable atmosphere the resistance from any metal connector or wand to ground should be less than 106 ohm. If only a thin inner layer of a solids transfer hose is semiconductive it should be ensured that abrasion does not cause an unacceptable increase of resistance.
Sensitive Gas
A gas that is much more likely to cause a failure in a flame arrester test because of its low AIT or other characteristics not obvious from its IEC standard MESG value
Sensitivity
The sensitivity of a measure to a parameter is defined as the change in the measure per unit change in that parameter.
Sensitizer
A substance which on first exposure causes little or no reaction in man or test animals, but which on repeated exposure may cause a marked response not necessarily limited to the contact site. Skin sensitization is the most common form of sensitization in the industrial setting, although respiratory sensitization to a few chemicals is also know to occur. Importance: Knowing that a substance is a sensitizer allows you to be aware of the signs and symptoms of overexposure.
Sensitizer
A chemical that causes a substantial proportion of exposed people or animals to develop an allergic reaction in normal tissue after repeated exposure to the chemical.
Separate
Means accessible only to plant personnel responsible for the proper operation and maintenance of Emerency Shutdown Device.
Sequence
An arrangement of control devices, wiring, or software programming such that the operation of connected equipment must follow a predetermined order.
Sequence Control
Automatic control of a series of operations in a predetermined order. A system of control in which a series of machine movements occurs in a desired order, the completion of one movement initiating the next, and in which the extent of the movements is not specified by numerical input data.
Sequential Control System
A control system in which the individual steps are processed in a predetermined order, progression from one sequence step to the next being dependent on defined conditions being satisfied. Such a system may be time-dependent, in which the step transition conditions are functions of time only; on external-event dependent, where the conditions are functions of Input signals only; or combinations of these (and perhaps more complex) conditions.
Sequential Function Chart (SFC)
A graphical representation of a Sequential Program consisting of interconnected steps, actions and directed links with transition conditions.
Sequential Program
A plan which prescribes the actions on a system in a predetermined order and in which some actions depend on the execution of preceding ones or on the fulfillment of certain conditions.
Serial (Data Transmission)
A system wherein the bits of a character occur serially in time, implies only a single transmission channel.
Serious Injury
The classification for an occupational injury which includes: (a) all disabling work injuries and (b) non-disabling work injuries as follows: (1) eye injuries requiring treatment by a physician, (2) fractures, (3) injuries requiring hospitalization, (4) loss of consciousness, (5) injuries requiring treatment by a doctor and (6) injuries requiring restriction of motion or work, or assignment to another job.
Severity
The maximum credible consequences or effects, assuming no safeguards are in place.