Specialty Gas Equipment Glossary A ATOMIC WEIGHT – The relative weight of an atom BURST PRESSURE – A design test pressure which of an element, compared to carbon-12. Equivalent allows for permanent deformation and leakage, ABSOLUTE PRESSURE – Pressure measured with to the sum of protons and neutrons in the nucleus. but parts must remain assembled (i.e., no sudden respect to total vacuum. Equal to the sum of a ruptures). Normal industry standard is 4 times pressure gauge reading and atmospheric pressure. AUTOIGNITION TEMPERATURE – The minimum (400%) of maximum operating pressure. See also temperature for a material to ignite without an ABSOLUTE ZERO – The minimum point in thermo- “PROOF PRESSURE” and “MAXIMUM OPERATING external ignition source. dynamic temperature scale (-273.16ºC or PRESSURE.” -459.69ºF). AZEOTROPIC MIXTURE (AZEOTROPE) – A liquid C mixture of two or more substances which ABSORPTION – The penetration of matter in bulk behaves like a single substance in that the vapor CP (CHEMICALLY PURE) – Denotes a high purity into other matter, as in the dissolving of a gas in produced by partial evaporation of liquid has the gas, but the actual % purity will depend on the liquid. same composition as the liquid. The constant boil- particular gas. ACCURACY – The degree of agreement of a mea- ing mixture exhibits either a maximum or mini- CALIBRATION – Comparison of a measurement sured value with the true or expected value of the mum boiling point as compared with that of other standard or instrument with another standard or quantity of concern. mixtures of the same substances. instrument to report or eliminate by adjustment ADSORPTION – Adherence of the atoms, ions or B any variation (deviation) in the accuracy of the item being compared. molecules of a gas or liquid to the surface of BACK-PRESSURE REGULATOR – A pressure regu- another substance, called the adsorbent. lator which controls upstream (inlet) pressure. CALIBRATION GAS – A gas or gas mixture of Molecular sieves are adsorbents. Similar in function to a relief valve. accurately known composition used as a compar- ative standard in analytical instrumentation. AEROBIC MIXTURE – A biological atmospheric gas BALANCED POPPET (BALANCED VALVE; BAL- mixture, containing Oxygen, used as a controlled ANCED STEM) – A valve which has been designed CALORIE – The amount of heat required to raise atmosphere for the growth of aerobic bacteria. to be pressure balanced; hence the valve spring the temperature of one gram of water one degree ACGIH (AMERICAN CONFERENCE OF GOVERNMENTAL provides the shutoff force. Used essentially to Celsius. reduce or minimize decaying inlet pressure effect. INDUSTRIAL HYGIENISTS) – This Conference is a CARRIER GAS – Gas used with gas chromatogra- professional society, not an official Government BIOLOGICAL ATMOSPHERE GASES – Mixtures, phy to carry the sample through the system. agency. It is an organization devoted to the devel- usually of air or oxygen with varying amounts of CATALYST – A substance that initiates a chemical opment of administrative and technical aspects of carbon dioxide, for growth of biological cultures. If reaction and allows it to proceed under different worker protection. oxygen is present it is Aerobic, if not it is conditions than otherwise possible. ANAEROBIC MIXTURE – A biological atmospheric Anaerobic. CERTIFIED MIXTURE – A mixture whose concentra- gas mixture, oxygen free, used as a controlled BLEND – See “MIXTURES.” atmosphere for the growth of anaerobic bacteria. tion is determined by analysis and comparison with BOILING POINT – The temperature at which the a Primary Standard of NIST reference material. ANALYTICAL ACCURACY – Guaranteed accuracy of vapor pressure of the liquid is equal to the CGA NUMBER – Cylinder/container valve outlet reported analytical result. prevalling pressure of the atmosphere. The normal connection number assigned by the Compressed boiling point is the temperature at which the ANHYDROUS – A descriptive term meaning with- Gas Association. CGA numbers are detailed in CGA vapor pressure of the liquid is 14.7 psia (1 atm). out water (ie: anhydrous ammonia). Standard V-1. BONNET (SPRING HOUSING) – The part of a regu- ANNEALING GAS – A hydrogen and nitrogen mixture CHECK VALVE – A mechanical device that allows lator which houses the control spring. used to provide a reducing atmosphere during heat- flow of gas in only one predetermined direction, to ing of metals to render them less brittle on cooling. BRASS – copper/zinc alloys of varying composi- prevent backflow of gas or contaminants. tion. Some brass also contains low percentages of ASPHYXIANT GAS – A gas which has little or no CAS (CHEMICAL ABSTRACT SERVICES) – CAS other elements such as manganese, aluminum, positive toxic effect but which can bring about numbers represent chemical substances recorded silicon, lead and tin. unconsciousness and death by replacing air and in the CAS Chemical Registry System. This num- thus depriving an organism of oxygen. BTU (BRITISH THERMAL UNIT) – The quantity of bering system identifies chemical substances by ATTACHED POPPET (TIED-SEAT; TIED-DIAPHRAGM) – heat required to raise the temperature of one an unambiguous computer language description A feature of certain regulators whereby the stem pound of water one degree Fahrenheit at or near of its molecular structure, including all stereo- (poppet) is physically attached to the diaphragm. its point of maximum density (39.1ºF). chemical detail. The CAS number, which has no chemical significance, is simply a number BURSTING DISK (FRANGIBLE DISK) – A metal disk ATMOSPHERIC PRESSURE – The amount of force assigned in sequential order to each substance as which is part of a safety device, and which is exerted by the Earth’s atmosphere. Equal to 14.7 it enters the Registry System. All specific sub- intended to burst and allow gas to escape within psia or 0 psig. stances reported in the world’s scientific and predetermined pressure limits to prevent rupture of technical literature, and indexed in Chemical AA (ATOMIC ABSORPTION) – An analytical instru- the device it is installed on. Similar in function to a Abstracts (CA) since 1965 (when the Registry mental method that is normally used to measure safety relief valve, except it has no reseal capability. metal concentrations. System began), are included in this master file. Specialty Gas Equipment

CHEMILUMINESCENCE – A species which chemi- matter how great the pressure. See also “CRITI- DIAPHRAGM VALVE – Packless valve using a metal cally absorbs and emits light (usually at low tem- CAL TEMPERATURE” and “CRITICAL PRESSURE.” diaphragm to prevent leakage of gas through the peratures). valve stem. There is no direct connection between CRITICAL PRESSURE – At the “CRITICAL TEMPER- the hand wheel and the valve stem. CHROMATOGRAM – The record produced by the ATURE,” the highest pressure at which a pure gas or liquid chromatograph. It is also a measure material can exist as a gas in equilibrium with its DIP TUBE – See “EDUCTOR TUBE.” of instrument performance. liquid. DOPANT – An impurity usually added in small COEFFICIENT OF FLOW (Cv) – Defined as the actual CRITICAL TEMPERATURE – The temperature above amounts to a pure substance to alter its properties. flow performance in U.S. gallons of water per which a gas cannot be liquefied by pressure DOT ID NUMBERS – These are product identifica- minute at 60ºF when inlet pressure (P1) is 1 psig alone. At this temperature, there is no distinction tion numbers, assigned by the Department of and outlet pressure (P2) is atmospheric (14.7 psia). between liquid and vapor, both having the same Transportation (DOT) to assist members of fire density and constituting one homogenous system. COLUMN – Part of the gas chromatography sys- and police departments in using the DOT tem where the separation of the sample takes CRYOGENIC LIQUID – A liquid having a normal Emergency Response Guidebook. DOT ID numbers place (can be packed or capillary). boiling point below -240ºF (-151.11ºC) contain two letters followed by four digits. The prefix UN (for United Nations) identifies products COMBUSTION – An exothermic oxidation reaction CRYOGENIC LIQUID CONTAINER – An insulated recognized throughout the world. Gaseous nitro- which may occur with any organic compound, as container designed to store, handle, and transport gen, for example, is identified as UN 1066. well as with certain elements. liquids having boiling points below -130ºF. DROOP – The decrease in outlet set pressure of a COMPRESSED GAS – (1) A gas or mixture of CYLINDER – A container designed to hold com- pressure regulator which results from an increase gases having, in a container, an absolute pressure pressed gases or liquefied compressed gases. in flow rate. Essentially the reverse of lockup. See exceeding 40 psi at 70ºF; or (2) a gas or mixture Cylinders are manufactured and tested according also “LOCKUP.” of gases having, in a container, an absolute pres- to DOT/CTC/MEX specifications. sure exceeding 104 psi at 130ºF, regardless of the DRUG GAS – A gas or gas mixture that is inhaled pressure at 70ºF; or (3) a liquid flammable materi- D and has a physiological effect upon the body. al having a vapor pressure exceeding 40 psi at DEHYDRATION – Removal of one or more mole- 100ºF as determined by ASTM D-323–72. cules of water from a chemical compound. E ECD (ELECTRON CAPTURE DETECTOR) – A gas DELAYED (CHRONIC) HEALTH HAZARD – See “EPA CGA (COMPRESSED GAS ASSOCIATION) – This is a chromatography detector that is very sensitive to HAZARD CATEGORIES.” nonprofit technical association whose member- halogen-containing compounds. Uses P-5, nitro- ship includes many corporations active in all DELIVERY PRESSURE – See “OUTLET PRESSURE.” gen or helium. phases of the compressed gas industry. Founded in 1913, the CGA uses the experience and knowl- DENSITY – The ratio of the amount of anything EDUCTOR (LIQUID DELIVERY) TUBE – A tube inside edge of its members to promote industrywide per unit volume; e.g., mass of any substance per a cylinder or container attached to the cylinder standards and procedures for safety in the manu- unit volume at any definite temperature. It is usu- valve which allows liquid product withdrawal from facture, storage, transport, and use of com- ally expressed in pounds per cubic foot (lbs/ft3). the cylinder. See also “SPECIFIC GRAVITY.” pressed gases. EFFLUENT SPLITTER – The part of the analytical CORROSIVE – The ability of a chemical compound DEPARTMENT OF TRANSPORTATION (DOT) – This instrument that splits the effluent stream into to attack, and produce irreversible damage to, is a government agency whose Title 49, Code of multiple detectors or some to vent for a lower vol- human tissues, such as eyes, skin or mucous Federal Regulations, regulates the transport of ume of effluent. hazardous materials. membranes. Also, the ability of a chemical com- EPA (ENVIRONMENTAL PROTECTION AGENCY) – pound to attack and eat away rubber, metal and DEVICE GAS MIXTURE – A gas mixture that is used This is a government agency that establishes other substances. for the calibration of medical diagnostic equip- environmental standards within the United States. ment. The gas may enter the body, but its action is CRACKING PRESSURE – A term used in back EPA HAZARD CATEGORIES – The hazard cate- not dependent upon its being metabolized. pressure control only (e.g., back pressure regula- gories used throughout this manual as defined tors, relief valves), for determining the inlet pres- DEWAR – Vessel which contains cryogenic lique- under EPA SARA Title III and 1910.1200 of Title 29 sure at which flow starts. fied gases. of the Code of Federal Regulations are as follows: CREEP – Any increase in outlet pressure of a DEW POINT – The temperature at which the lique- pressure regulator subsequent to lockup, usually • Immediate (Acute) Health Hazard, including faction of vapor begins; the term is usually seen as a long term, slow pressure increase. This applied to condensation of moisture from the highly toxic, corrosive, toxic, irritant, sensi- generally indicates a seat leak, which is an abnor- water vapor in the atmosphere. tizer, and other hazardous chemicals which mal condition. cause an adverse effect to a target organ, DISS (DIAMETER INDEX SAFETY SYSTEM) – DISS CRITICAL DENSITY – The density of a pure materi- and manifest themselves within a short peri- outlet valves are generally used with high-purity al at its critical temperature and critical pressure. od of time following a one time, high expo- products, toxics, and corrosives. Valves equipped sure to the substance. CRITICAL POINT – The transition point at which with DISS outlet assignment provide a metal-to- the liquid and gaseous states of a substance metal seal that creates low particle generation, a merge into each other. It is the temperature above permeation-free environment, and good leak which a substance cannot exist in two phases, no integrity. Specialty Gas Equipment

• Delayed (Chronic) Health Hazard, including FLAMMABLE RANGE – The range over which a INERT – A material which, under normal tempera- carcinogens and other hazardous chemicals gas at normal temperature and pressure will form tures and pressures, does not react with other which cause an adverse effect to a target a flammable mixture with air. materials. organ and manifest themselves after a long FLASH POINT – The lowest temperature at which IR (INFRARED) – An area of the spectrum at longer period of time following or during repeated a flammable liquid will give off enough vapor at or wavelength than red light. Used in analysis as contacts with the substance. near its surface to form an ignitable mixture with certain compounds absorb Infrared light at char- air. acteristic wavelengths. • Fire Hazard, including flammable, combustible pyrophoric, and oxidizer. FLOW CAPACITY – The maximum flow capability INHIBITOR – A compound (usually organic) that of a control device established at a specific set of retards or stops an undesired chemical reaction • Sudden Release of Pressure Hazard, conditions. such as corrosion, oxidation or polymerization. including explosive and compressed gas. FLOWMETER – An instrument used to measure INLET PRESSURE (P1; SUPPLY PRESSURE; • Reactive Hazard, including unstable reactive, flow rate. Measurement is either by a floating ball UPSTREAM PRESSURE) – The pressure of the fluid organic peroxide, and water reactive. (Rotameter) or by heat transfer (Mass Flowmeter). to the supply connection of a control device. EPA PROTOCOL GASES – Gas mixtures used for FLUID – Any material or substance that changes INORGANIC SUBSTANCE – Substances that do not the calibration of stationary source continuous shape uniformly in response to an external force contain carbon in their chemical structure. emission monitors (CEMs). The mixtures are man- imposed upon it. The term applies to liquids, IRRITANT – The ability of a chemical, which is not ufactured according to procedures laid down by gases, and finely divided solids. corrosive, to cause a reversible inflammatory the EPA and are traceable to NIST SRMs. FREEZING POINT – The temperature at which a effect on living tissue by chemical action at the EXPOSURE LIMITS – Concentrations of substances liquid solidifies. It is the temperature at which the site of contact. (and conditions) under which it is believed that liquid and solid states of a substance are in equi- ISOTHERMAL INTEGRAL HEAT OF ADSORPTION – nearly all workers may be repeatedly exposed day librium at a given pressure. See “HEAT OF ADSORPTION.” after day without adverse effects. “ACGIH” limits G are called “TLV” and “OSHA” exposure limits are ISOTOPES – Forms of an element that differ from called “PEL.” See “THRESHOLD LIMIT VALUE.” GMIS (GAS MANUFACTURER’S INTERMEDIATE one another in the mass of their atoms and in the STANDARD) – An internal standard, directly trace- properties dependent on that mass. Having the F able to a NIST SRM, used in the certification of same atomic number and the same number of FID DETECTOR – FLAME IONIZATION DETECTOR – mixtures. valence electrons, isotopes occupy the some posi- A gas chromatography detector that looks for GROSS WEIGHT – The weight of a package plus tion in the periodic table and have identical prop- substances that can be ionized in a flame. the weight of its contents. erties. They are distinguishable only by the small Commonly uses helium, hydrogen, and air. differences in atomic weight or by radioactive H FILLING DENSITY – The percent ratio of the weight transformations. of liquified compressed gas in a container to the HALOCARBONS – Any hydrocarbon combined with K weight of water that the container will hold at 60ºF. any of the five (F2, Cl2, Br, I, At) elements in the VIIA group of the periodic table. KELVIN (K) – A unit of temperature related to the FIRE HAZARD – See “EPA HAZARD CATEGORIES.” triple point of water. HEAT OF ADSORPTION – The total heat involved in FLAME PHOTOMETRY – An instrument utilizing a the adsorption process from zero adsorbate load- L flame for the analysis of metals, particularly in ing to some final adsorbate loading at a constant LIQUEFIED COMPRESSED GAS – A gas which, medical applications. Usually uses propane or temperature (also called isothermal integral heat under the charged pressure, is partially liquid at a methane. of adsorption). temperature of 70ºF (21.1ºC). FLAMMABLE GAS – (1) A gas that, at ambient HEAT OF FUSION – The heat energy required to LIQUID DENSITY – The ratio of the mass of a liq- temperature and pressure, forms a flammable transform one MOLE of substance from the liquid uid per unit volume at any definite temperature. It mixture with air at a concentration of 13% by vol- phase to the vapor phase at one atmosphere of is usually expressed in pounds per gallon or ume or less; or (2) a gas that, at ambient temper- pressure. pounds per cubic foot. ature and pressure, forms a range of flammable mixtures with air wider than 12% by volume, HYDROCARBON – An organic compound contain- LOCKUP – The increase in outlet pressure of a regardless of the lower limit. ing carbon and hydrogen. pressure regulator that occurs when flow is stopped. Essentially the reverse of DROOP. FLAMMABLE LIMITS – The concentration of flam- I mable vapor in air, oxygen, or other oxidants that I/M GASES – Calibration gas mixtures used for LEL (LOWER EXPLOSIVE LIMIT) – The minimum will propagate flame upon contact when provided testing of mobile source emissions. Typically they percent by volume of a gas which, when mixed with air at normal temperature and pressure, will with a source of ignition. The lower explosive limit contain CO, CO2, Propane, and NO, are traceable (LEL) is the concentration below which a flame to NIST SRMs. form a flammable mixture. See “FLAMMABLE will not propagate; the upper explosive limit (UEL) GAS.” is the concentration above which a flame will not IMMEDIATE (ACUTE) HEALTH HAZARD – See “EPA propagate. A change in temperature or pressure HAZARD CATEGORIES.” may alter the flammable limits. Specialty Gas Equipment

M NON-LIQUEFIED GAS – A substance that exists POLYMERIZATION – A chemical reaction, usually entirely as a gas at 70ºF. carried out with a catalyst, heat or light, and often MANIFOLD – A series of connectors to a common under high pressure, in which a large number of outlet allowing several cylinders to be used simul- NORMAL BOILING POINT (nbp) – The temperature relatively simple molecules combine to form a taneously. at which the vapor pressure of a liquid reaches chain-like macromolecule. 760 mm of mercury. MSDS (MATERIAL SAFETY DATA SHEET) – An MSDS ppb (PARTS PER BILLION) – Equal to is a substance fact sheet containing characteristics NORMAL EVAPORATION RATE (NER) – The degree 0.0000001%. and hazards of specific hazardous industrial materi- of product loss from a cryogenic liquid container al. Also, these data sheets provide precautionary due to heat leak into the container as designed. ppm (PARTS PER MILLION) – A convenient means information on safe handling of the material, as well The NER is checked by measuring the amount of for expressing low concentrations. As applied to as emergency and first aid procedures. product loss over a specified time and serves to gases, ppm stands for moles per million moles. confirm whether the insulation is still effective. ppm by weight is expressed as pounds per million MAXIMUM OPERATING PRESSURE – The maxi- pounds. ppm by volume is usually expressed in mum allowable use pressure for which a system NORMAL TEMPERATURE AND PRESSURE (NTP) – cubic feet per million cubic feet. Equal to is designed. Also referred to as “WORKING PRES- A gas industry reference base. Normal tempera- 0.00001%. SURE.” ture is 70ºF. Normal pressure is one atmosphere, or 14.696 psia. PRIMARY STANDARD – A standard whose concen- MELTING POINT – The temperature at which the tration can be traced directly to a fundamental solid and liquid phase of a substance are in equi- O unit of measurement such as mass. Standard of librium (normally specified at one atm). OSHA (OCCUPATIONAL SAFETY AND HEALTH highest accuracy and precision. METERING VALVE – A valve capable of accurately ADMINISTRATION) – An organization within the PROOF PRESSURE – A test pressure applied to controlling the flow of a gas. Usually a needle U.S. Department of Labor which sets standards control devices to verify structural integrity. No valve. for employers to ensure safe and healthful work- ing conditions for employees. deformation or excessive leakage is permitted at MICRON – One millionth of a meter. this pressure and the control device must function OUTLET PRESSURE (P2; DELIVERY PRESSURE; normally subsequent to this test. Normal industry MIXTURE – Any combination of two or more DOWNSTREAM PRESSURE) – The pressure of the standard is 1.5 times (150%) of “WORKING PRES- chemicals if the combination is not, in whole or in fluid from the discharge connection of a control SURE.” See also “BURST PRESSURE” and “MAXI- part, the result of a chemical reaction. device. MUM OPERATING PRESSURE.” MOLE – The weight of a substance equal numeri- OXIDIZING AGENT – A chemical reagent which PURGE – Flushing of cylinders, manifolds or other cally to its molecular weight. A gram-mole is the causes oxidation of other substances and is equipment with an inert gas to remove contami- weight in grams equal to the molecular weight; a thereby reduced. nation or residue. Purging improves efficiency of pound-mole is the weight in pounds equal to the the process. molecular weight. P PYROPHORIC – The ability of a chemical to ignite MOLECULAR WEIGHT – The sum of the atomic PACKED VALVE – A valve that relies on a com- spontaneously in air at a temperature of 130ºF or weights of all the constituent atoms in the mole- pressed packing to prevent leakage of gas below. cule of an element or a compound. between the valve stem and body. PYROPHORIC GAS – A gas that can spontaneously N PACKLESS VALVE – A valve that uses a metal seal, such as a diaphragm, to seal the body from the self-ignite when exposed to normal atmospheric Ϫ9 NANOGRAM (ng) – One billionth of a gram (10 ). valve stem and prevent any gas leakage. conditions. Ϫ9 NANOMETER (m) – One billionth of a meter (10 ). PARTIAL PRESSURE – In any gas mixture the total R NF (NATIONAL FORMULARY) – A supplement to pressure is equal to the sum of the pressures RARE GAS – Refers to those constituents of air the United States Pharmacopoeia. (partial) which each gas would exert were it alone which comprise less than 1% of air and are gen- in the volume occupied by the “MIXTURE.” erally considered inert, such as argon, helium, NEEDLE VALVE – Valve using a needle-shaped krypton, neon and xenon. stem moving into and closing a small orifice. PEL (PERMISSIBLE EXPOSURE LIMITS) – See Accurately meters flow. “EXPOSURE LIMIT.” REACTIVE HAZARD – See “EPA HAZARD.” NIST (NATIONAL INSTITUTE OF STANDARDS AND PHYSICAL HAZARD – Descriptive of a chemical for REFERENCE GAS – A gas or gas mixture with pre- TECHNOLOGY) – Government organization that which there is scientifically valid evidence that it cisely defined composition used as a reference supplies Standard Reference Materials – “THE is a combustible liquid, a compressed gas, explo- standard in instrumental analysis. NATIONAL STANDARD.” sive, flammable, an organic peroxide, an oxidizer, pyrophoric, unstable reactive or water reactive. RELIEF VALVE – A type of pressure relief device NTRM (NIST TRACEABLE REFERENCE MATERIAL) – which is designed to relieve excessive pressure, A standard produced by a gas manufacturer and POISON – A substance that in relatively small and to reclose and reseal, to prevent further flow certified by NIST. Considered by NIST and EPA to doses has an action, when it is ingested by, of gas from the cylinder after reseating pressure be equivalent to an SRM. injected into, inhaled or absorbed by, or applied to has been achieved. a living organism, that either destroys life or NOx – General symbol for Oxides of Nitrogen. Can impairs seriously the function of one or more include Nitric Oxide, Nitrogen Dioxide and organs or tissues. Nitrogen Trioxide. Specialty Gas Equipment

RFO (RESTRICTIVE FLOW ORIFICE) – A safety SPECIFIC VOLUME (Sp. Vol.) – Volume occupied by TLV-TWA (THRESHOLD LIMIT VALUE – TIME device placed in the outlet of a cylinder valve a unit mass of a substance at a given tempera- WEIGHTED AVERAGE) – Refers to the time-weight- intended to limit the release rate of a hazardous ture. It is usually expressed in cubic feet per ed average concentration for a normal 8 hour gas to a maximum specified range in the event of pound or gallons per pound. workday and a 40-hour workweek to which nearly the inadvertent opening of the valve or the failure all workers may be repeatedly exposed, day after SPRING HOUSING – See “BONNET.” of the system downstream of the valve outlet. day, without adverse effect. SRM (STANDARD REFERENCE MATERIAL) – A ROTAMETER – See “FLOWMETER.” TIED-DIAPHRAGM – See “ATTACHED POPPET.” national standard produced by NIST. The highest S level of standard available. TIED-SEAT – See “ATTACHED POPPET.” SAFETY RELIEF DEVICE – A safety device usually STAINLESS STEEL – Alloy steels containing high THC (TOTAL HYDROCARBON CONTENT) – THC is incorporated in a cylinder valve and actuated by percentages of chromium, from less than 10% to used to describe the quantity of the hydrocarbon excessive pressure or temperature, or both, at more than 25%. impurities present. Usually expressed as methane predetermined limits to avoid failure of the pres- equivalents. sure vessel. STP (STANDARD TEMPERATURE AND PRESSURE) – An internationally accepted reference base. TOXIC – A substance that has the ability to pro- SELF-RELIEVING (SELF-VENTING) – A feature Standard temperature is 0º C. Standard pressure is duce injurious or lethal effects through its chemi- incorporated in certain pressure reducing regula- one atmosphere or 14.6960 psia. cal interaction with the body. tors which enables the unit to relieve the outlet pressure when adjusted in the decrease direction. SUBLIMATION – The direct passage of a sub- TRIPLE POINT (tp) – The definite temperature and stance from solid to vapor without appearing in pressure for a pure substance at which the three SENSITIZER – The ability of a chemical to cause a the intermediate (liquid) state. An example is solid phases (solid, liquid, and vapor) coexist in equilib- substantial proportion of exposed people or ani- carbon dioxide (dry ice) which vaporizes at room rium as an invariant system. mals to develop an allergic reaction in normal tis- temperature. sue after repeated exposure to the chemical. U SUDDEN RELEASE OF PRESSURE HAZARD – See UN (UNITED NATIONS) – See “DOT ID NUMBERS.” STEL (SHORT TERM EXPOSURE LIMIT) – See “EPA HAZARD CATEGORIES.” “THRESHOLD LIMIT VALUE – SHORT TERM EXPO- USP (UNITED STATES PHARMACOPOEIA) – The SURE LIMIT.” SUCK BACK – The reverse flow of gas or liquid. official publication for drug product standards. Usually refers to the back flow of liquid into a gas SUPPLY PRESSURE – See “INLET PRESSURE.” cylinder. UNSTABLE REACTIVE – The ability of a chemical in the pure state, or as produced or transported, to SKIN – The skin designation, used with the terms T vigorously polymerize, decompose, condense, or TLV-TWA and OSHA-PEL, indicates that cutaneous TARE WEIGHT – The weight of an empty cylinder become self-reactive under conditions of shock, absorption may contribute to the overall exposure. without cap and valve. pressure or temperature. SOLVENT – A substance capable of dissolving TLV (THRESHOLD LIMIT VALUE) – TLVs are mea- UPSTREAM PRESSURE – See “INLET PRESSURE.” another substance (solute) to form a uniformly sures of toxicity established by the ACGIH. The TLV dispersed mixture (solution) at the molecular or of a substance refers, in general, to airborne con- V ionic size level. centrations at or below which nearly all workers VAPOR PRESSURE – The pressure characteristic SPAN GAS – Gases which are used as a reference may be repeatedly exposed without adverse at any given temperature of a vapor in equilibrium point to span an analyzer. effect. with its liquid or solid form. SPECIFIC GRAVITY (Sp. Gr.) – The ratio of the THRESHOLD LIMIT VALUE – CEILING (TLV-CEIL- W weight of one substance compared to the weight ING)-Refers to an airborne concentration that WATER REACTIVE – The ability of a chemical to of an equal volume of another substance which is should not be exceeded, even instantaneously. react with water to release a gas that is either used as a standard. Usually gases are compared TLV-STEL (THRESHOLD LIMIT VALUE – SHORT flammable or presents a health hazard. to air (air = 1) while liquids and solids are com- TERM EXPOSURE LIMIT) – Refers to a 15-minute WORKING PRESSURE – See “MAXIMUM OPERAT- pared to water (H20 = 1). time-weighted average exposure which should ING PRESSURE.” SPECIFIC HEAT – Amount of heat required to raise not be exceeded at any time during a workday, a unit mass of a substance one degree of temper- even if the time-weighted average is within the Z ature at either constant pressure (Cp) or constant TLV. It supplements the 8-hour TLV-TWA for cer- ZERO GAS – Gases which are used as a reference volume (Cv). tain substances that produce acute effects on point to “zero” an analyzer. high, short-term exposure. SPECIFIC HEAT RATIO – The ratio of “SPECIFIC HEAT” at constant pressure (0º C) to the specific heat at constant volume (Cv).