The terms and abbreviations listed below are confusing, arcane, ambiguous and otherwise useless. C: Ceiling Value. For example, Toluene-2, 4-diisocyanate (TDI) has a Permissible Exposure Limit PEL of (C) 0.02 ppm; Code: On some MSDS's that come out of the Department of Defense (DoD) HMIRS database, we have seen codes associated with almost every field that have are typically "M" or "T". These do not appear to be HMIRS Health Characteristic Codes. We hear directly (third-hand) that in this post-9/11 world the DoD does not wish us to know what the codes represent, even though they have released the codes for each entry!; EST: Eastern Standard Time Estimated (could also be "Established" when written "Not Est"); MST: Mountain Standard Time Mist; N/A (sometimes "NA"): Not Applicable, Not Available; N/Ap (sometimes "NA"): Not Applicable; N/Av (sometimes "NA"): Not Available; ND: North Dakota None Determined or Not Determined; NE: Nebraska North-East None Established; NEGL: Negligee Negligent Negligible; NF: None Found; N/K (sometimes "NK"): Not Known; N/P (sometimes "NP"): Not Provided; REC: (sometimes "R") Recommended. Do not confuse with RTECS; S/A (sometimes "SA") Simple Asphyxiant; SKN: Skin; SUP DAT: "whaSup (with) 'Dat?" Possibly "Supply Missing Data" or "Supplementary Data". Apparently a database artact? TS: Trade Secret; UNK: "Unknown"; UNR: "Unreported"; WATER: Z26020 (or other Z-type numbers), found under the solubility description. This is an error on certain outdated Sigma-Aldrich MSDS's; looks like their computer forgot to put in the correct value; Wilson RISK Scale: as described in a separate entry, this is a proprietary hazard rating system for which we can find no detailed information. Without such information, this (or any other) rating system is essentially useless. Your opinion may dfer, of course. There is no good reason to abbreviate terms on an MSDS Material Safety Data Sheet! MSDS Relevance: Beware, the folks that use these may have meant something else