Glossary of Terms: P

Pa2Hr Pascal squared hours
A measure of the noise exposure of a person. An alternative means of stating how much noise to which a person has been exposed. A noise exposure level of 85 dBA is the same as 1 Pa2hr.
Particulate matter
A suspension of fine solid or liquid particles in air, such as dust, fog, fume, mist, smoke or sprays. Particulate matter suspended in air is commonly known as an aerosol.
Particulate
Airborne material with a relatively fixed shape and volume such as dust, mist, smoke and fume
Pascal (Pa)
Unit of pressure equal to 1 Newton per square meter.
Pdose
Projected dose, a sound level meter measurement. It is the calculated dose for a projected amount of time, based on actual dose measurement from the actual run time.
Peak (Lpk, L_Pk)
Peak is the highest instantaneous sound level that the microphone detects. Peak is detected independently of the unit’s Response Time setting (Fast or Slow).
Perimeter monitoring
Monitoring the outer edge of a plant or storage area as opposed to monitoring specific points.
Permissible Exposure Limit (PEL)
An exposure limit that is published and enforced by OSHA as a legal standard.
Personal monitoring
A technique used to determine an individual’s personal exposure to a chemical, physical or biological agent. This is done by means of a sampling device worn on the worker’s body (e.g., personal monitor). The monitoring of hazardous chemicals is done at the breathing zone; the monitoring of noise is done at the ears.
Personal protective equipment (PPE)
Devices worn by the worker to protect against hazards in the environment. Respirators, gloves, and hearing protectors are examples.
pH
Means used to express the degree of acidity or alkalinity of a solution with neutrality indicated as seven.
Physical agent
A source of energy (for example, noise, radiation, vibration, heat) that affects the body, a part of the body, or any of its functions. The effects may be beneficial or harmful.
PLC
Programmable Logic Controller.
Plenum
A compartment or chamber enclosing a pollutant source and connected by ductwork to an air cleaner
Point detection
Detecting or measuring gas at a fixed point/position.
Poison resistant
Capability of a catalytic sensor to reduce the effect of inhibiting substances or contaminants, such as silicones.
Polymerization
A chemical reaction in which two or more small molecules (monomers) combine to form larger molecules (polymers) that contain repeating structural units of the original molecules. A hazardous polymerization is the above reaction, with an uncontrolled release of energy.
PPB
Parts per billion concentrations in the atmosphere.
PPM
Parts per million concentrations in the atmosphere.
Preamplifier (Preamp)
On some sound level meters a preamplifier is used to connect the microphone to the unit.
Pressure drop
the difference in static pressure measured at two locations due to friction or turbulence
Projected time
The variable amount of time used to make a projected dose calculation from an actual dose measurement.
Projected TWA
A sound level meter measurement that is the calculated TWA for a projected amount of time, based on actual noise measurement from the actual run time.
PSI
Pounds per square inch (for MSDS purposes) is the pressure a material exerts on the walls of a confining vessel or enclosure. For technical accuracy, pressure must be expressed as psig (pounds per square inch gauge) or psia (pounds per square absolute; that is, gauge pressure plus sea level atmospheric pressure, or psig plus approximately 14.7 pounds per square inch).