متدهای استاندارد سایت OSHA جهت اندازه گیری فلزات

Metals Sampling
 
A. Air Samples
Collect metal fumes using a three-stage 37-millimeter (mm), 0.8-micrometer (μm) mixed cellulose ester filter (MCEF) cassette. Use pre-weighed PVC filters for those substances listed in Appendix II:1-4. See OSHA’s Chemical Sampling Information file for appropriate sampling rates and times. Be careful not to overload the filter. See the discussion on filter overloading in the GENERAL MONITORING REQUIREMENTS AND GUIDELINES, SAMPLING PROTOCOL section of this document.

When sampling for welding fumes, the filter cassette must be placed inside the welding helmet to obtain an accurate measurement of the employee's exposure. Welding fume samples are normally taken using a 37-mm MCEF and cassette. If these cassettes will not fit inside the helmet, 25-mm MCEF and cassettes can be used. Extra care must be taken not to overload the smaller 25-mm MCEF when sampling.

NOTE: The practice of placing the sampling device inside personal protective equipment (PPE) applies only to PPE that is not intended to provide respiratory protection such as welding helmets or face shields. This sampling is performed to determine if respiratory protection is needed. If the PPE has supplied air, such as a welding hood or an abrasive blasting hood, then the sample is placed outside the PPE.

B. Bulk Samples
Bulk samples are sometimes taken to document the source of the material present in the air. Always attempt to take representative samples for bulk analysis. SLTC analysts will make a reasonable attempt to homogenize samples submitted by CSHOs, however, excessive sample quantities and highly non-homogenous samples complicate this process. Ideally, bulk samples should contain a minimum of approximately 200 mg, but less than a gram, shipped in glass 20-mL scintillation vials with Polytetrafluroethylene (PTFE) lined caps. However, it is recognized that these recommended limitations may not always prove practical, and the professional judgment of the CSHO always takes precedence.

FIGURE II: 1–3. EXPLODED VIEW OF A 37-mm THREE-PIECE CASSETTE AND
ASSEMBLY ILLUSTRATING PLACEMENT OF THE BACK–UP PAD

C. Metal Analysis
The SLTC is capable of analyzing a variety of metals in specific compatible combinations depending on the ability of the analytical method to simultaneously dissolve the metals of interest in a given acid matrix. Some of the current analyte/matrix combinations are listed below and are defined by specific OSHA sampling and analytical methods. Refer to OSHA’s Chemical Sampling Information file for the most up-to-date analyte/method combinations.

The following combination of 13 metal analytes can be analyzed simultaneously by Inductively Coupled Plasma (ICP) using OSHA Method 125G.

Antimony
Beryllium
Cadmium
Chromium
Cobalt
Copper
Iron
Lead
Manganese
Molybdenum
Nickel
Vanadium
Zinc

NOTE: The above combination of analytes has been historically referred to as "ICP" for welding fume samples. Where one or more of the analytes are requested for a given filter sample, a full ICP analysis may be conducted, however, CSHOs should specify metals of the most interest in the event samples cannot be analyzed by this method or any other multi-element method. Sometimes, alternative types of samples (e.g., samples taken during abrasive blasting operations) may not be analyzed using OSHA Method 125G (ICP) because of analytical difficulties encountered with sample characteristics, heavy sample loadings, analyte solubility limitations, and instrumental limitations. Some of these problematic samples and analytes can sometimes be analyzed using other multi-element methods listed below or with one of the OSHA Method 121 procedures originally designed for individual metal determinations (e.g., Pb, Cd, Fe). Refer directly to OSHA Method 121 to interpret the complex choices and compatibilities of a host of assorted analytes and their various preparation techniques. When questions of analytical capabilities arise, CSHOs are encouraged to contact SLTC spectroscopy experts for further guidance and discussion of analytical options to suit specific compliance monitoring needs.

The SLTC can also analyze the following combination of metal analytes historically referred to as "solder " using OSHA Method 206:

Antimony
Beryllium
Cadmium
Copper
Lead
Silver
Tin
Zinc

The following combination of metal analytes can be analyzed by OSHA Method 105:

Arsenic
Cadmium
Copper
Iron
Lead
Zinc

The following combination of metal analytes can be analyzed by OSHA Method 1006 (air samples only):

Arsenic
Cadmium
Copper
Cobalt
Lead
Nickel