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D6494-22 – Standard Test Method Technical Guide
🎯 Scope and Applicability
ASTM D6494-22 covers the determination of asphalt fume particulate matter as the benzene soluble fraction, alongside total particulate matter weight, in workplace atmospheres. It utilizes a polytetrafluoroethylene (PTFE) filter methodology adapted from NIOSH Method 5023 (withdrawn) and OSHA Method 58, specifically modified to reduce background contamination for better reproducibility. This method is compatible with high-flow personal sampling pumps operating between 0.5 and 2.0 L/min for both personal and area monitoring.
The sampling approach can be configured for time-weighted average (TWA) exposures and short-term exposure limits (STEL). The applicable TWA concentration range is 0.2 to 2.0 mg/m³. All values stated in SI units are regarded as standard.
⚠️ Safety Responsibility: This standard does not address all safety concerns. The user is responsible for establishing appropriate safety, health, and environmental practices. Refer to Section 9 for specific precautionary statements. Note that candidate solvents for benzene replacement have been identified, but substitution requires further validation with field data.
⚙️ Sampling Procedure and Key Parameters
The procedure requires rigorous adherence to established practices for sampling planning (D1357), flow rate adjustment of personal sampling pumps (D5337), and sample chain-of-custody (D4840). The primary collection media is a PTFE filter. Guide D6062 should be consulted for proper selection of personal samplers for health-related aerosol fractions. Furthermore, Guide D8358 addresses the assessment and inclusion of wall deposits in the analysis of single-stage samplers, which is critical for accurate mass determination.
| 🟦 Parameter | 📏 Specification / Range |
|---|---|
| 📐 Sampling Media | Polytetrafluoroethylene (PTFE) Filter |
| ⚡ Flow Rate Range | 0.5 to 2.0 L/min |
| 🎯 Sample Type | Time-Weighted Average (TWA) & Short-Term Exposure Limit (STEL) |
| 📊 TWA Concentration Range | 0.2 to 2.0 mg/m³ |
📊 Key Measured Properties and Analytical Data
The key measured property is the benzene soluble fraction of asphalt fume particulate matter. The adaptation of the hybrid NIOSH/OSHA methodology in this standard emphasizes low background contamination for high reproducibility. Laboratories conducting this analysis should align with the principles of ISO/IEC 17025 for general competence. The standard was developed in accordance with WTO TBT Committee principles.
💡 Solvent Consideration: A study (Sutter, B., et al., Ann. Occup. Hyg.) has suggested candidate solvents for benzene replacement. While a less toxic solvent is desirable, any substitution for benzene in this extraction process must undergo validation with suitable field data to ensure comparable performance.
| 📄 Referenced Document | 📌 Description / Purpose |
|---|---|
| 🏛️ NIOSH Method 5042 | Benzene-Soluble Fraction and Total Particulate (Asphalt Fume) |
| 🔬 OSHA Method 58 | Coal Tar Pitch Volatiles |
| 📏 ASTM D1356 | Terminology for Sampling and Analysis of Atmospheres |
| ✅ ISO/IEC 17025 | General Requirements for Testing & Calibration Laboratories |
❓ Frequently Asked Questions
🔍 What is the primary purpose of ASTM D6494-22?
This method is specifically designed for the determination of asphalt fume particulate matter (measured as the benzene soluble fraction) and total particulate weight in workplace atmospheres using a PTFE filter media.
💡 What are the recommended flow rate and sampling media?
Personal sampling pumps must maintain a flow rate between 0.5 and 2.0 L/min, collecting samples onto a polytetrafluoroethylene (PTFE) filter. It is capable of generating time-weighted average (TWA) and short-term exposure limit (STEL) samples.
⚡ What is the specific concentration range for the TWA sample?
The applicable concentration range for the TWA sample strictly defined in the standard is from 0.2 to 2.0 mg/m³.
📌 Why was this standard adapted from NIOSH and OSHA methods?
The adaptation from NIOSH Method 5023/5042 and OSHA Method 58 was specifically performed to reduce the level of background contamination, providing better overall reproducibility of results.