m/sec:  Meters per Second. A measurement of air velocity.

m3/min:  See cubic metres per minute.

M3/min M3/hr:  Volume flow rate measured in cubic meters per minute (or per hour).

Macaque Monkeys:  The macaques are a subgroup of the old world monkey and baboon family, that are widely distributed in Africa, central and southeast Asia, southern China and Japan. This group includes the rhesus and cynomolgus monkeys – two types of macaques used in biomedical research.

Mach Number:  The ratio of the actual velocity at a given point to the velocity of sound in the same gas at the conditions existing at this point. These are known as local conditions.

Magnehelic® Gauge:  Registered trade name for a diaphragm activated dial gauge that measures changes in air pressure. These readings can translate into several measurements that include filter resistance, air velocity, fan and blower pressures, and furnace draft.

Main Vent (or Stack): Principal vent to which branch vents may be connected. See Stack.

Maintenance:   Care and upkeep of the surrounding environment.

Maintenance Medication: Medication given on a regular basis to help prevent symptoms.

Major Source: A stationary facility that emits a regulated pollutant in an amount exceeding the threshold level depending on the location of the facility and attainment with regard to air quality status. (See Source.)

Make-up Air: Air supplied to a space to replace exhausted air.

Malaise:   A vague feeling of discomfort or uneasiness.

Male IPS: Pipe connection where the threads are on the outside of the fitting. See MIP.

Male Threads: See MIP.

Malignant:  As applied to a tumor. Cancerous and capable of undergoing metastasis, or invasion of surrounding tissue.

Malignant Hyperthermia:  An inherited condition in humans and some animals that results in an uncontrolled increase in body temperature upon exposure to certain anesthetics. Halothane is a potent trigger of malignant hyperthermia in susceptible animals or people. At one time, the genetic trait was common in commercial pigs, but it has been almost eliminated through genetic selection.

Malodor:  Nasty or foul smell noticeable by humans.

Man Way:  An inspection cover or port in an air receiver tank.

Mannequin:  An animal mannequin is an anatomical model used for teaching.

Manometer: Measuring device for small gas pressures.

Mansard Roof: A roof which rises by inclined planes from all four sides of a building. The sloping roofs on all four sides have two pitches, the lower pitch usually very steep and the upper pitch less steep.

Mantel: The shelf above a fireplace. Also used in referring to the decorative trim around a fireplace opening.

Manufactured Wood: A wood product such as a truss, beam, Glue Lam or joist which is manufactured out of smaller wood pieces and glued or mechanically fastened to form a larger piece. Often used to create a stronger member which may use less wood. See Oriented Strand Board.

Manufacturers Specifications: The written installation and/or maintenance instructions which are developed by the manufacturer of a product and which may have to be followed in order to maintain the product warrantee.

Map of Radon Zones: A U.S. EPA publication depicting areas of differing radon potential in both map form and in state specific booklets.

Mariculture:  The culture of plants and animals in marine waters independent of any pollution source.

Marsh:  A frequently or continually inundated wetland characterized by emergent herbaceous vegetation adapted to saturated soil conditions.

Martin’s Diameter:  Statistical diameter used in particle size analysis; the mean length of the line, parallel to the microscope traverse, diving each particle into two equal diameters.

Masking:   The phenomenon where a quality in a mixture obscures one or more other qualities in it.

Masking Agent:  A substance used to cover or hide a malodor, does not remove the problem.

Mason’s Hammer (Bricklayer’s Hammer): Tool shaped like a chisel to trim brick or stone.

Masonry: Concrete, concrete block brick, adobe, stone and other similar materials.

Masonry Primer: An asphalt-based primer used to prepare masonry surfaces for bonding with other asphalt products.

Master Recycling Permit:  A permit issued to a supplier or a distributor, or both, of recycled water that includes waste discharge requirements prescribed pursuant to Section 13263 and water recycling requirements prescribed pursuant to Section 13523.1.

Mass: The quantity of matter in body as measured by the ratio of the force required to produce a unit acceleration.

Mass-Area-to-Glazing-Area Ratio: The ratio of the total surface area of massive elements to the glazing area. Massive elements including in this definition are all floors, walls ceilings, or other interior objects with densities comparable to high-density concrete provided their surfaces are exposed and located in a room that is at least partially illuminated by direct solar gains.

Mass Distribution:  Relative frequency distribution of mass within a particle size distribution. Sometimes presented as cumulative percentage undersize.

Mass Transfer Rate:  Measurement of the movement of matter as a function of atoms etc.

Mast Cell:  A connective tissue cell that contains coarse, basophilic, metachromatic secretory granules that contain, among other pharmacologic agents, heparin, histamine, and eosinophilic chemotactic factor. These cells are involved in immediate hypersensitivity reactions and play a role in the regulation of the composition of ground substance.  Syn: granule cell of connective tissue, labrocyte, mastocyte, tissue basophil.  [G. Mastszellen, well-fed c. (Ehrlich)].

Mastic: A thick creamy substance used to seal seams and cracks in building materials.

Mastitis:  Inflammation of the mammary glands.

Matched Lumber: Lumber that is dressed and shaped on one edge in a grooved pattern and on the other in a tongued pattern.
Matched System:  System comprised of multiple Trane components designed and engineered to work seamlessly together to enhance overall performance, reliability and efficiency.

Material:  (a) In common usage: (1) the substance or substances of which a thing is made or composed (2) substantial; (b) matter of any kind or description which is subject to regulation as waste, or any material dredged from the navigable waters of the United States. See also, Dredged Material.

Material Safety Data Sheets (MSDS): Product safety information sheets prepared by manufacturers and marketers of products containing toxic chemicals. These sheets can be obtained by requesting them from the manufacturer or marketer. Some stores, such as hardware stores, may have material safety data sheets on hand for products they sell.

Mattress Cover:  Protective anti-allergenic cover preventing bed-bug ingestion / inhalation.

MAWP:  Maximum allowable working pressure. This data is found on the pressure vessel nameplate and is the maximum pressure at which the lowest set safety valve must be set (stamped).

Maximal Oxygen Uptake: A person’s highest rate of oxygen consumption. This measurement is usually expressed in milliliters of oxygen per kilogram of body weight per minute.

Maximally Exposed Individual (MEI):  Hypothetical member of the public at a fixed location who, over an entire year, receives the maximum effective dose equivalent (summed over all pathways) from a given source of radionuclide releases to air. Generally, the MEI is different for each source at a site.

Maximum Available Control Technology (MACT): The emission standard for sources of air pollution requiring the maximum reduction of hazardous emissions, taking cost and feasibility into account. Under the Clean Air Act Amendments of 1990, the MACT must not be less than the average emission level achieved by controls on the best performing 12 percent of existing sources, by category of industrial and utility sources.

Maximum Contaminant Level (MCL):  Enforceable drinking water standards adopted either by the California Department of Health Services or the federal EPA. It is the maximum permissible level of a contaminant in drinking water.

Maximum Occupancy Load: The maximum number of people permitted in a room. It is measured per foot for each width of exit door. The maximum is 50 per foot of exit.

Maximum Operating Pressure:  The highest operating pressure the system or component is designed to withstand.

Maximum Use Concentration (MUC):  The maximum concentration of a hazardous substance from which a user can be expected to be protected when wearing a given respirator; usually calculated by multiplying the Occupational Exposure Limit for the substance by the Assigned Protection Factor for the respirator (OEL X APF = MUC).

Mayonnaise:  The oily condensate discharged by lubricated air compressors. The name is derived from the appearance of the condensate. Under normal conditions oily condensate should just be cloudy, like a small amount of milk in a bucket of water. When a lubricated compressor goes wrong, then the condensate becomes thick and sticky. In fact almost identical in appearance to the name it has been given.

MCLs:   Maximum Contaminant Levels.

MCS:   See “Multiple Chemical Sensitivity.”

MD:  Refers to the “machine-direction” when manufacturing filtration roll stock.

MDR TB: Multidrug-resistant TB. TB that is resistant to Isoniazid and Rifampin. More difficult to treat than drug-susceptible TB.

Mean: Average.

Mean Efficiency Rating:  The measurement of the average efficiency of a filter medium using the Multi-Pass Test where the average filtration (BETA) ration equals 2.0.

Mean Flow Pore Measurement:  It is calculated as the diameter of the pore of a membrane partially voided of liquid such that air flow of the partially wetted membrane is equal to 1/2 the dry air flow. (Theoretical diameter of the mean pore).

Mean Peak Flow Rate: The average of several peak expiratory flow rates; expressed in liters per minute.

Mean Radiant Temperature (MRT): The area weighted mean temperature of all surrounding surfaces, i.e. sum of (s.t)/ sum of (s), where 't' is the temperature of each surface of angular area 's'. Also the temperature of a uniform black enclosure in which a solid body or occupant would exchange the same amount or radiant heat as in the existing nonuniform environment. It is an approximate indication of the effect that the surface temperatures of surrounding objects have on human comfort.

Mechanical Air Purifier: The most common air filters available on the market; Mechanical Air Purifiers use a fan to draw air through a filter. Common mechanical air filters are activated carbon filters, high density fiber filters, and HEPA filters.

Mechanical Efficiency:  The ratio of the indicated power to shaft input.

Mechanical Systems: A term widely used in commercial and industrial construction, referring to all the mechanical components of the building. i.e. plumbing, heating, ventilation, air conditioning and heat recovery.

Mechanically Ventilated Crawl Space: A system designed to increase ventilation within a crawlspace, achieve higher air pressure in the crawlspace relative to air pressure in the soil beneath the crawlspace, or achieve lower air pressure in the crawlspace relative to air pressure in the living spaces, by use of a fan.

Mechanics Lien: A lien on real property, created by statue in many years, in favor of persons supplying labor or materials for a building or structure for the value of labor or materials supplied by them. In some jurisdictions, a mechanics lien also exists for the value of professional services. Clear title to the property cannot be obtained until the claim for the labor, materials, or professional services is settled. Timely filing is essential to support the encumbrance, and prescribed filing dates vary by jurisdiction.

Media: Specific environments — air, water, soil — which are the subject of regulatory concern and activities.

Media Migration:  Carry over of particles or contaminant from the filter or other filter materials into the clean side of the air flow.

Median: The middle value in a population distribution, above and below which lie an equal number of individual values; midpoint.

Medical History: A list of a person’s previous illnesses, present conditions, symptoms, medications and health risk factors.

Medical Referral: A doctor’s recommendation that a patient see a qualified medical professional, often a specialist, to review their health status and determine whether medical treatment is needed or whether a particular course of exercise and/or diet change is safe.

Medication Plan: A specific plan to achieve and maintain control of asthma based on use of controller and reliever medications in a stepwise approach. A medication plan also includes instructions on how to recognize worsening of asthma and what actions to take. Also known as an asthma plan.

Medium:  Is singular for media and is the material . . . paper, wire, cellulose or a combination . . . from which the filter element is made and which does the actual filtration or separation.

Megawatt (MW): One million watts.

Megawatthour (MWh): One million watt-hours.

Melt Point: The temperature at which solid asphalt becomes a liquid.

Meltblown:  A nonwoven manufacturing process for filtration media, where a molten polymer is extruded out of an orifice with high-velocity air to create fine fibers. The fibers can create roll stock or be spray-spun onto porous tubes to create a finished filter.

Melting Point: The temperature at which a solid becomes a liquid. At this temperature, the solid and the liquid have the same vapor pressure.

Membrane: A generic term relating to a variety of sheet goods used for certain built-up roofing repairs and application.

Membrane Dryer:  Reduce dew point by passing compressed air through a bundle of hollow membrane fibers; water vapor and a portion of the compressed air then permeate the membrane walls and vent to atmosphere.

Membrane Filter:  Continuous matrix with fine pores of defined size or a film allowing for the diffusion of a fluid through its structure; sometimes referred to as a dense film in the case where no pores are present.

Mercury/Mercury Compounds: Mercury is a toxic heavy metal that is a byproduct of the combustion of fossil fuels, especially coal. Mercury and
compounds containing mercury can accumulate in the environment and are highly toxic to humans and animals if inhaled or swallowed. Exposure can permanently damage the brain, kidneys, and fetuses.

MERV (Minimum Efficiency Reporting Values) Rating:  A system for rating air filters according to their average particle size efficiency on a scale from 1-16 with 16 being the highest capture efficiency for average particles in the 0.3 to 1.0 micron range. The rating is derived from a test method developed by the American Society of Heating, Refrigerating, and Air Conditioning Engineers (ASHRAE).

MERV 12 (Minimum Efficiency Reporting Value): Assigned by ASHRAE based on a filter’s ability to remove dust, mold spores, pollen, pet dander, dust mite particles and other tiny particulates from the air

Mesh: A term referring to a woven filtration medium, typically wire cloth or monofilament woven fabric.

Mesh Count:  Number of openings or fractions of openings in a lineal inch of wire cloth or monofilament woven fabric.

Mesh Opening:  Mesh opening is the difference between wires measured in the warp and weft direction in the projected plane of the wire mesh.

Mesh Size:  Mesh is the number of openings in a square inch of screen or sieve. It is equal to the square of the number of strands of metal or plastic screening per lineal inch. Standard US mesh screen # 16 equates to a 1.19 millimeter particle diameter, mesh size #40 is 0.42 millimeters.

Mesosphere: The layer of the Earth’s atmosphere above the stratosphere and below the thermosphere. It is between 35 and 60 miles from the Earth.

Meta-analysis: A method of analysis which combines the results of a number of surveys to investigate the underlying processes.

Metabolic Rate: The rate of heat production by the body when engaged in various tasks, often defined in terms of the resting metabolism (Mets).

Metabolism: The body’s use of oxygen and food to produce energy.

Metals: Any class of chemical elements with specific physical and chemical qualities. The ratios of metal elements such as potassium and iron have been shown to be an indicator of wood combustion.

Metal Edge: Brake metal or metal extrusions which are secured at the perimeter of the roof to form a weather-tight seal.

Metal Lath: Sheets of metal that are slit and drawn out to form openings. Used as a plaster base for walls and ceilings and as reinforcing over other forms of plaster base.

Metastasis:  Transfer of the causal agent (cell or microorganism) of a disease from a primary focus to a distant one through the blood or lymphatic vessels. Also, spread of malignancy from site of primary cancer to secondary sites.

Metazoan:  Multicellular organism (e.g. worms). A protozoan is a unicellular organism.

Meter:  A metric unit of length, equal to about 39 inches.

Metered-Dose Inhaler (MDI):  A device used to administer a defined dose of medication for inhalation; used frequently in the treatment of asthma and other respiratory conditions.

Methacoline: A type of chemical used in challenge testing. Everybody’s airways respond to it, but asthmatic’s airways respond much more and at lower doses.

Methane (CH4): A hydrocarbon that is a greenhouse gas with a global warming potential most recently estimated at 23 times that of carbon dioxide (CO2). Methane is produced through anaerobic (without oxygen) decomposition of waste in landfills, animal digestion, decomposition of animal wastes, production and distribution of natural gas and petroleum, coal production, and incomplete fossil fuel combustion. The global warming potential (GWP) is from the Intergovernmental Panel on Climate Change’s (IPCC's) Third Assessment Report (TAR).

Method Detection Limit (MDL):  The minimum concentration of a substance that can be measured and reported with 99% confidence that the analyte concentration is greater than zero, as defined in 40 CFR PART 136 Appendix B.

Methyl Tertiary Butyl Ether (MTBE): An ether compound added to gasoline to provide oxygen and enhance complete combustion. MTBE is being phased out of California’s gasoline.

Metric Units:  Except for temperature for which specific equations apply, U.S. customary units can be determined from metric units by multiplying the metric units by the U.S. customary equivalent. Similarly, metric units can be determined from U.S. customary equivalent units by multiplying the U.S. customary units by the metric equivalent. 

Mg/M3:   Milligrams per cubic meter.

MHEA: Mobile Home Energy Audit.  A software tool that predicts manufactured home energy consumption and recommends weatherization retrofit measures.

Micro-Climate: The climate in the immediate vicinity of a building.

Micro-Stat:  The secondary filter in Data Clean’s environmental vacuums. This filter is typically made from fiberglass batting, similar to building insulation. The microstat filter traps all dirt larger than 3.0 microns in size.

Microbes:   Microscopic organisms such as algae, insects, viruses, bacteria, fungi, and protozoa, some of which cause diseases.

Microbiologicals:   See “Biological Contaminants.”

Microenvironment:   A particular part of the large environment that is in some way whole by itself. Used to describe a subset of the global environment such as the indoor environment.

Microgram per gram (µg/g):  A measurable unit of concentration for a solid. A mercury level of 1.0 µg/g means that one microgram (one millionth of a gram) of mercury was detected in one gram of sample. It is equivalent to one part per million.

Microfiltration (MF):  Used for clarification, sterilization, to detect or analyze bacteria and other organisms and particulate matter. Separation of particles ranging from 0.1μm to 10μm.

Microgram (µg):  One-millionth of a gram (3.5 x 10-8 oz. 0.000000035 oz.).

Microisolator (cages):  The term “microisolator” describes laboratory animal cages that have an air filter in a frame covering the entire top of the cage, used to minimize contamination of the animals in the cage.

Microlam: A manufactured structural wood beam. It is constructed of pressure and adhesive bonded wood strands of wood. They have a higher strength rating than solid

Micrometer:  (µm, often abbreviated as um, micron or µ) A unit of measurement of length, equal to one-millionth of a meter (approximately 0.00003937 inch).

Micron:   A unit of linear measure equal to one millionth of a meter, or one thousandth of a millimeter.

Micron Rating:  A measurement applied to filters or filter media to indicate the particle size at which suspended solids above that size will be removed.

Microorganism:   A microscopic organism, especially a bacterium, fungus, or protozoan.

Microporous Membrane: Thin polymeric films (e.g. 0.001 to 0.005” thick) often with millions or pores per square inch, aligned as a torturous path, allowing for the passage of a fluid to remove solids. Often used for sterilizing filtration and other fine filtration purposes. Considered a surface filter medium.

Microprocessor Controls:  A control system that uses computer logic to operate and monitor an air conditioning system. Microprocessor controls are commonly used on modern precision air conditioning systems to maintain precise control of temperature and humidity and to monitor the units operation.

Microscopic:  Too small to be seen with the naked eye.

Migration:  Movement of a substance from one place to another through natural processes.

Mil:  One thousandth of an inch.

Mil Thickness: Measurement used to determine thickness of a coating. 1 mil = .001 inch (1/1000).

Milar (Mylar): Plastic, transparent copies of a blueprint.

Mildew:  A common name for mold or fungi; often used in reference to fungal growth on bathroom tiles and fixtures. 

Millibar:  A unit of atmospheric pressure equal to 1,000 dynes per sq. cm. or about 1/32 in. of mercury.

Milligram per Kilogram (mg/Kg):  A unit of concentration for a solid. A mercury level of 1.0 mg/kg in fish means that one milligram (one thousandth of a gram) of mercury was found in each kilogram of sampled fish. (A kilogram is 1,000 grams or approximately 2.2 pounds). Also equals one part per million.

Milligram per Liter (mg/L):  A unit of the concentration of water or wastewater constituent.  It is 0.001 gm of the constituent in 1,000 ml of water.  One mg/L is approximately equal to one part per million.

Milligrams per Cubic Meter (mg/m3):  Unit used to measure air concentrations of dusts, gases, mists, and fumes.

Milliliter (mL):  A metric unit used to measure volume. One milliliter equals one cubic centimeter.

Millimeter of Mercury (mmHg): The unit of pressure equal to the pressure exerted by a column of liquid mercury one millimeter high at a standard temperature.

Millimetre of Mercury (mmHg):  A measure of pressure expressed in metric units; see pressure.

Million Gallons per Day (MGD):  A measurement of water flow equal to about 0.5 cubic feet per second.

Millwork: Generally all building materials made of finished wood and manufactured in millwork plants and planing mills are included under the term “millwork.” It includes such items as inside and outside doors, window and doorframes, blinds, porchwork, mantels, panelwork, stairways, moldings, and interior trim. It normally does not include flooring, ceiling, or siding.

Mineral Oil:  The most commonly used lubricating oil for compressors.

Mineral Spirits: A by-product of petroleum, clear in color, used as a solvent for asphalt coatings.

Mineral Stabilizers: Finely ground limestone, slate, traprock or other inert materials added to asphalt coatings for durability and increased resistance to fire and weathering.

Mineral-Surfaced Roofing: Asphalt shingles and roll roofing that are covered with granules.

Mini-Environment:  An environment that provides localized control of airborne contaminants by means of an enclosure designed to isolate product-handling areas from personnel and the surrounding room environment.

Minimum Bubble Point Pressure:  It is a diffusional flow pressure just before the onset of bulk flow. Minimum critical bubble point pressure: a filter specification derived from diffusional flow, bubble point curves for many filters.

Minimum Detectable Amount (MDA):  The minimum datable amount (MDA) is the smallest activity or mass of an analyte in a sample or person that can be detected with an acceptable level of uncertainty.

Minimum Level (ML):  The concentrations at which the entire analytical system must give a recognizable signal and acceptable calibration point. The ML is the concentration in a sample that is equivalent to the concentration of the lowest calibration standard analyzed by a specific analytical procedure, assuming that all the method-specified sample weights, volumes and processing steps have been followed.

Minispread: A smaller variation of a widespread faucet with separate spout and handles designed small enough to fit 4” center-to-center faucet holes.

MIP (Male Iron Pipe): Standard threads that are on the outside of a pipe or fitting.

Miscible: Capable of being mixed with other substances.

Mist:   Liquid particles measuring between 40 and 500 microns. By contrast, particles making up fog are less than 40 microns.

Miter Joint: The joint of two pieces at an angle that bisects the joining angle. For example, the miter joint at the side and head casing at a door opening is made at a 45° angle.

Mitigate: To make less severe or to mollify.

Mitigation:  To make less severe; lessen the hardship.

Mixed Cellulose Esters:  Synthetic materials derived from naturally occurring cellulose. Materials used in the manufacture of membrane filters. Mixed cellulose esters membranes are used in a wide variety of applications, such as bacteria concentration in water analysis and air sampling.

Mixed Systems: A solar heating system that combines two or more passive solar heating types.

Mixed Waste:  Waste that has the properties of both hazardous and radioactive waste.

Mixed-Mode Systems: Heating or cooling systems which combine passive and mechanical systems.

Mixing Valve: A valve that mixes hot and cold water in the valve to obtain a set temperature prior to delivery.

Mixing Zone:  A designated volume of a receiving water where wastewaters and receiving water mix.  Allocation of a mixing zone provides limited dilution of a wastewater discharge before certain water quality objectives must be met.

MMCFD:  Millions of cubic feet per 24 hour.

mmHg:  See millimetre of mercury.

Mobile Home Aluminum Roof Coating: Durable one-coat application prolongs the life of mobile home roofs while reflecting sun's rays and providing a decorative surface. Reduces energy costs.

Mobile Sources:  Moving objects that release pollution; mobile sources include cars, trucks, buses, planes, trains, motorcycles and gasoline-powered lawn mowers.  Mobile sources are divided into two groups:  road vehicles, which include cars, trucks and buses, and non-road vehicles, which include trains, planes and lawn mowers.

Mock-Up Testing: Controlled air, water and structural performance testing of existing or new glazing systems.

Model Code Organizations: Includes the following agencies and the model building codes they promulgate:

• Building Officials and Code Administrators International, Inc. (BOCA National Building Code/1993 and BOCA National Mechanical Code/1993);
• International Conference of Building Officials (Uniform Building Code/1991 and Uniform Mechanical Code/1991);
• Southern Building Code Congress, International, Inc. (Standard Building Code/1991 and Standard Mechanical Code/1991);
• Council of American Building Officials (CABO One- and Two-Family Dwelling Code/1992 and CABO Model Energy Code/1993).

Modified Bitumen Roof: A roof covering that is typically composed of a factory-fabricated composite sheet consisting of a copolymer-modified bitumen, often reinforced with polyester and/or fiberglass, and installed in one or more plies. The membrane is commonly surfaced with field-applied coatings, factory-applied granules or metal foil. The roofing system may incorporate rigid insulation.
Modulating Control:  Compressor controls will run the compressor at varying loads to accommodate demand variations. Running a compressor at less than full load results in a drop in compressor efficiency and thus an increase in operating costs.

Modulating Unload:  The air compressor continues to run and air supply is matched to the demand by partial unloading. This can be accomplished by a regulator controlled floating inlet or by step unloading.

Modulus: Stress at a given strain. Also tensile strength at a given elongation.

Moisture Content of Wood: Weight of the water contained in the wood, usually expressed as a percentage of the weight of the oven-dry wood.

Moisture Holding Capacity:  The amount of liquid that can be held against gravity by waste materials without generating free liquid.

Moisture Separator:  A unit designed to separate condensate from the compressed air stream.

Moisture Trap:  A device designed to enable accumulated liquids to be held for draining in a compressed air system.

Molarity:  The term used to indicate the concentration of dissolved substance in a given solution. The measurement is in moles of dissolved substance per liter of solution.

Mold:  Pronunciation (mōld).  (1.) A filamentous fungus, generally appearing as a circular colony that may be cottony, wooly, or glabrous, but with filaments that are not organized into large fruiting bodies, such as mushrooms. (2.) A shaped receptacle into which wax is pressed or fluid plaster is poured in making a cast. (3.) To shape a mass of plastic material according to a definite pattern. (4.) To change in shape; denoting especially the adaptation of the fetal head to the pelvic canal. (5.) The term used to specify the shape of an artificial tooth (or teeth).  Syn: mould.

Mold Spores: Moulds and fungi reproduce by sending out showers of spores into the air. About 20% of people who suffer from airborne allergies are affected by these mould spores. Most will be allergic to more common triggers too and so, for them, the mould allergy is an additional complication rather than the main cause of symptoms. Moulds can grow anywhere, indoors and out. They are most at home in damp conditions – the kitchen and bathroom and in wooden window frames, the soil of houseplants and under wallpaper throughout the house. Outside, moulds are plentiful in the soil, in rotting wood and leaves, grass cuttings and compost heaps.

Molding: A wood strip having a coned or projecting surface used for decorative purposes, e.g., door and window trim.

Molecular Sieves:  A solid adsorbent used for drying compressed air.

Molecular Theory:  All matter consists of molecules which are in constant motion, but which are held together by molecular forces. In a solid the molecules are closely packed and arranged in such a pattern that the influence of the molecular forces is very strong. This gives the solid its consistency and form. Molecular motion consists largely of oscillations around points of equilibrium. In a liquid the molecules are about as close as in a solid, but they are not arranged in a lattice and the cohesive forces are weaker. The molecules are more mobile in relation to each other, whereby the characteristic liquid phase develops; the liquid accommodated itself to the walls of the containing vessel, and its free surface aligns itself horizontally in response to the force of gravity. In a gas, however, the molecules are farther apart, and they move freely about each other since the molecular forces are not as strong. A gas therefore expands through space and mixes with other gasses present. The total volume of the molecules in a gas is very small in relation to the volume of the gas. A gas can therefore be compressed into a small part of its original volume.

Molecules:  The smallest physical units of a substance that still retain the chemical properties of that chemical substance; molecules are the building blocks of a cell. Some examples are proteins, fats, carbohydrates, and nucleic acids.

Monitoring (monitor): Measurement of the types and amounts of air pollution. The 1990 Clean Air Act requires states to monitor community air in polluted areas to check on whether the areas are being cleaned up according to schedules set out in the law. Also, the 1990 Clean Air Act requires certain large polluters to perform enhanced monitoring to provide an accurate picture of their pollutant releases such as keeping detailed records, participating in periodic inspections, and installing Continuous Emissions Monitoring Systems (CEMS).

Monitoring Well:  Specially constructed wells used for collecting representative samples of ground water for water quality testing.

Monofilament:  Single, large continuous filament of a synthetic yarn. Similar to fishing line in cross-section.
 
Monofilament Woven Fabric:  Woven fabric from monofilament yarns used as a screen or surface filter. Often used in sifting, belting, medical filters etc. Most common yarns are from polyester, polypropylene and nylon.

Monopost: Adjustable metal column used to support a beam or bearing point. Normally 11 gauge or Schedule 40 metal, and determined by the structural engineer.

Montreal Protocol:  This landmark agreement initially required a production and consumption freeze. The Montreal Protocal called for a stepwise reduction and eventual production phase out of various ozone depleting substances in developed countries.

Mopping: In roofing, a layer of hot bitumen mopped between plies of roofing felt. Full mopping is the application of bitumen by mopping in such a manner that the surface being mopped is entirely coated with a reasonably uniform coating. Spot Mopping is the procedure of applying hot bitumen in a random fashion of small daubs, as compared to full mopping. Sprinkle mopping is a special application of installing insulation to the decks. It is done by dipping a roof mop into hot bitumen and sprinkling the material onto the deck. Strip Mopping is the application of bitumen in parallel bands.

Morbidity:   The number of sick individuals or cases of disease in a population.

Mortality:   The number of individual deaths in a population.

Mortar: A mixture of sand, water, and cement used to bond bricks, stones, or blocks together.

Mortar Types: Type M is suitable for general use and is recommended specifically for masonry below grade and in contact with earth, such as foundations, retaining walls and walks. Type M is the strongest type. Type S is suitable for general use and is recommended where high resistance to lateral forces is required. Type N is suitable for general use in exposed masonry above grade and is recommended specifically for exterior walls subject to severe exposures. Type O is recommended for load-bearing walls of solid units where the compressive stresses do not exceed 100 lbs. per square inch and the masonry wall not be subjected to freezing and thawing in the presence of excessive moisture.
Mortgage: Loan secured by land.

Mortgage Broker: A broker who represents numerous lenders and helps consumers find affordable mortgages; the broker charges a fee only if the consumer finds a loan.

Mortgage Company: A company that borrows money from a bank, lends it to consumers to buy homes, then sells the loans to investors.

Mortgage Deed: Legal document establishing a loan on property.

Mortgage Origination Fee: A charge for work involved in preparing and servicing a mortgage application (usually one percent of the loan amount).

Mortgagee: The lender who makes the mortgage loan.

Mortise: A recessed area cut into the wood framing member where a hinge or wood tongue fits.

Most Penetrating Particle Size (MPPS):  The size of the particles that achieve maximum penetration of the filter medium. Particles that are smaller or larger than the most penetrating size exhibit a lower rate of penetration; the reduced penetration of the smaller particles is due to diffusion mechanisms, while for the large particles it is due to interception and inertial effects. The most penetrating size is a function of the structure of the filter medium, the velocity of the airflow through the filter, and the physical and chemical nature of the particles.

Most Probable Number (MPN):  An index of the number of coliform bacteria that, more probably than any other number, would give the results shown by laboratory examination; it is not an actual enumeration.

Motor:  A device that converts electrical energy into mechanical energy. A motor can operate on direct current (DC) or alternating current (AC) voltage supply, not both.

Motor Vehicle Fee Program: See AB 2766.

Mottling:  In spray painting applications, blotches of metallic or mica particles in a paint film caused by insufficient compressed air.

Mouthpiece:  The portion of a respirator that is held and sealed in the user’s mouth and is designed to be used in conjunction with a nose clamp; refer to CSA Z94.4 for the definition.

MPCV:  Combination minimum pressure valve and check valve.

MRI:  Magnetic Resonance Imaging (MRI) is a medical diagnostic technique that creates images of the body using nuclear magnetic resonance. When a patient is placed into the cylindrical magnet, the process follows three basic steps. First, MRI creates a magnetic steady state within the body using a magnetic field 30,000 times stronger than the earth’s magnetic field. Then MRI stimulates the body with radio waves to change the steady-state orientation of protons. It then stops the radio waves and “listens” to the body’s electromagnetic transmissions at a selected frequency. That signal is used to construct detailed internal images of the body using a computer program.

MSA:  Mine Safety Appliances Company.

MSDS:   Material Safety Data Sheet.

MSHA:  Mine Safety and Health Administration (USA).

Mu Receptors:  Opioid drugs bind to the mu receptors in the brain and nervous tissue.

MUC: Montréal Urban Community.

Mucolytic Agent: Medication that thins mucus secretions.

Mucormycosis:  A group of disease caused by the fungi belonging to the group Mucorales (Class Zygomycetes); such fungi may infect lungs, sinuses, mucous membranes, central nervous system, internal organs, and eyes.

Mucosa:  The mucosa is the membrane that lines body cavities including the intestine.

Mucous Membranes:  Lining of the hollow organs of the body, notably the nose, mouth, stomach, intestines, bronchial tubes, and urinary tract.

Mucus: A substance secreted by various tissues in the body (mucus membranes), made up of water, mucin, salts, and some cells. In the lungs, mucus serves to lubricate the insides of the airways and to trap foreign particles so that they can be coughed out. In asthma, however, an excess of mucus is produced and can actually block airways. Mucus also tends to be thicker and more viscous in asthmatics.

Mucus Clearing Device: A device used to loosen mucus in the airways so it can be coughed up more easily.

MUD:  Material to be filtered.

Mud Cracks: Cracks developing from the normal shrinkage of an emulsion coating when applied too heavily.

Mudsill: A wood foundation member, usually a pressure treated 2x4 or 2x6, bolted to the foundation and on which other framing members can be attached.

Mullens Burst Test:  A formal measurement where test specimen (filtration medium) sees a force, which cause it to burst.

Mullion: A vertical bar or divider in the frame between windows, doors, or other openings that supports and holds such items as panels, glass, sash, or sections of a curtain wall.

Multi-Pass: A test system designed to be representative of a typical hydraulic or lubricating circuit. Fresh contaminate is introduced in slurry form into a test reservoir, mixed with the fluid in the reservoir and pumped through the test filter; contaminate not captured by the filter is returned to the reservoir for another pass (or more) though the filter.

Multifilament:  A number of unbroken continuous fiber stands that run parallel to form a yarn. Typically used to manufacture a woven or knit fabric.

Multimedia Exposure: Exposure to a toxic substance from multiple pathways such as air, water, soil, food, and breast milk.

Multiple Chemical Sensitivity (MCS): A condition in which a person reports sensitivity or intolerance (as distinct from "allergic") to a number of chemicals and other irritants at very low concentrations. There are different views among medical professionals about the existence, causes, diagnosis, and treatment of this condition.

Multiple Triggers for Airborne Allergy:  With so many airborne allergy sufferers allergic either to house dust mite or to pollen, a very high proportion, over 50% of all airborne allergy sufferers, will be allergic to both. In practical terms this will mean that they may suffer airborne allergy symptoms all year round, with symptoms becoming noticeably worse during the pollen season.

Multistage Axial Compressor:   A machine having two or more impellers operating in series on a single shaft and in single casing.

Multistage Centrifugal Compressor:  A machine having two or more impellers operating in series on a single shaft and in single casing.

Multistage Compressor:  A machine employing two or more stages.

Muntins: Horizontal or vertical bars that divide the sash frame into smaller lights of glass. Muntins are smaller in dimensions and weight than mullions.

Muriatic Acid:  A diluted form of hydrochloric acid. Muriatic acid is used to test for the presence of sufficient seal on concrete. Improperly sealed concrete will have a noticeable chemical reaction with even a few drops of acid. A sufficient coating of seal will prevent the acid from interacting with the concrete.

Muscarinic Actions of Acetylcholine:  The muscarinic actions of acetylcholine include slowing the heart, increasing secretions from the salivary gland and respiratory tract. Thus, anti-muscarinic drugs used as preanesthetics block secretions that might clog up the respiratory track during anesthesia, and reduce the slowing of the heart rate. Muscarine is a mushroom-derived alkaloid that mimics certain actions of the neurotransmitter acetylcholine, hence the term “muscarinic” actions of acetylcholine.

Mushroom: An unacceptable occurrence when the top of a caisson concrete pier spreads out and hardens to become wider than the foundation wall thickness.

Mutagen:   Any substance e that can cause a change in genetic material.
 
Mutagenic: The ability of a chemical or physical agent to produce heritable changes in the DNA of living cells.

Mycellium:  The collective mass of hyphae (filamentous cells) comprising the body of most fungi and molds.  

Mycetoma:  Invasive fungal infection of subcutaneous tissues (under the skin).
Mycobacterium Tuberculosis (M. tuberculosis): The germ that causes TB.

Mycology:  The scientific study of fungi (Kingdom Fungi or Mycota).    

Mycosis:  An infection caused by fungi (mold) (pl. mycoses).  

Mycotoxicosis:  Any disease caused by fungal toxins (mycotoxins).  

Mycotoxins:  A diverse class of poisonous compounds produced by certain mushrooms and other fungi; mycotoxins are produced on the surface of mold spores and remain toxic even after the spore is dead.

Myringotomy:  Pronunciation (mir′in-got′ŏ-mē).  Incision of the tympanic membrane.
Syn: tympanotomy.  [myringo- + G. tomē, excision].