Glossary

The most frequently used exposure guideline term, is the average concentration of a chemical in air over the total exposure time – usually an 8-hour workday (OSHA PELs and ACGIH TLVs), and up to 10 hours in a 40hour workweek (NIOSH Recommended Exposure Limit (RELs).

A pair of thin-diameter insulated wires commonly used in telephone wiring. The wires are twisted around each other to minimize interference from other twisted pairs in the cable. Twisted pairs have less bandwidth than coaxial cable or optical fiber. Abbreviated UTP for Unshielded Twisted Pair. Synonymous: Twisted Wire Pair.

Two-stage tendering is a procedure typically used to achieve an early appointment of a contractor to a lump-sum contract. For the first stage, the objective is to competitively appoint, on the basis of limited information, a preferred contractor for further negotiation.

Separate beds or layers of cation and anion exchange resins. Results in lower purity than mixed-bed deionization but provides higher capacity in terms of throughput.

Thermostatted Well Plate

A Phenolic alpha amino acid; a precursor of the hormones epinephrine, norepinephrine, thyroxine, and triiodothyronine, and of the black pigment melanin.

The uracil residue in RNA.

Measured or specified concentration, in particles per cubic meter of air, including the ultrafine particles. ISO 14644-1, ISO 14644-3.NOTE: The U descriptor may be regarded as an upper limit for the averages at sampling locations (or as an upper confidence limit, depending upon the number of sampling locations used to characterize the cleanroom or clean zone). U descriptors cannot be used to define airborne particulate cleanliness classes, but they may be quoted independently or in conjunction with airborne particulate cleanliness classes.

Unidirectional Air Flow

Unloading Accumulation Table

User Acceptance Testing

A summary comprised of the critical testing results, actions and related conclusionsthat are generated during the testing process.

Uniform Building Code

Unrestricted Binary Code

Underpinning Contract

Unidirectional Airflow

Ultrafiltration

Urea-Formaldehyde

Uniform Federal Accessibility Standards

Composite Uncertainty Factor

Unidirectional Flow Hood

Ultrahigh-Molecular-Weight Polyethylene

United Kingdom

Underwriters Laboratories (Insurance Underwriters)