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D3959-91 – Standard Test Method Technical Guide
📐 Scope and Significance
This test method, designated D 3959-91 (Reapproved 2001), provides a standardized visual procedure for evaluating the discoloration sensitivity of rubber- and plastic-coated fabrics when exposed to tobacco smoke. It assesses both the degree of staining and the fabric’s ability to be effectively cleaned. The test is particularly useful for comparatively rating several different coated materials under identical environmental conditions.
⚙️ Apparatus and Materials
The smoking chamber consists of a modified desiccator, approximately 250 mm in diameter, fitted with a perforated porcelain plate (A). A metal cigarette holder (B) and a glass tube with a stopcock (C) are connected to a water-jet vacuum pump via a safety Woulff bottle. A drop collector (D) is placed beneath the cigarette. Test cigarettes must be approximately 85 mm long, unfiltered, and dried thoroughly in a desiccator with chalk for 16 hours prior to use. Standard 10 mm wide masking tape is used for mounting specimens.
| 🟦 Apparatus Component | 📏 Specification |
|---|---|
| Smoking Chamber | Modified desiccator, ~250 mm diameter, perforated porcelain plate |
| Vacuum System | Glass tube with stopcock, Woulff bottle, water-jet vacuum pump |
| Test Cigarettes | ~85 mm length, no filter, dried 16 hours over chalk |
| Cleaning Supplies | Ethanol (95%), sponge, filter paper for blotting |
📊 Test Procedure and Key Ratings
Three specimens, each precisely 25 by 60 mm, are cut from the coated fabric. After a standardized ethanol wipe and rinse, two specimens are mounted on a glass plate, leaving the third as an untreated control. The cigarette is lit, and the vacuum is carefully adjusted so the 60 mm exposed length burns completely in 1 minute ± 10 seconds. The stopcock is closed as the flame reaches the metal holder. After a 1-hour deposition period, the test cycle is repeated four times, followed by a final uninterrupted 24-hour smoke exposure. One smoked specimen is then cleaned using a strict protocol of ethanol wiping and wetting.
⚠️ Critical Timing Requirement: The cigarette burn time must be precisely controlled at 1 minute ± 10 seconds. The vacuum pump suction must be adjusted to maintain this rate, as deviations will invalidate the smoke deposition process.
The three test specimens—smoked only, smoked and cleaned, and the untreated control—are visually compared. The intensity of discoloration relative to the control is rated according to the following established scale:
| 📊 Rating | 🟦 Description |
|---|---|
| 1 | No discoloration |
| 2 | Slight discoloration |
| 3 | Medium discoloration |
| 4 | Heavy discoloration |
| 5 | Very heavy discoloration |
💡 Technical Tip: When comparing specimens, place them side-by-side on a neutral background. The subjective nature of the rating system requires consistent lighting and the use of the untested control specimen as the definitive baseline for “No discoloration.”
❓ Frequently Asked Questions
🔍 Why must the cigarettes be dried for 16 hours in a desiccator? Drying the cigarettes with chalk standardizes the moisture content of the tobacco. This ensures a consistent burning rate and smoke generation characteristics across all tests, eliminating humidity as a variable.
💡 What is the purpose of the 1-hour and 24-hour rest periods? The 1-hour pause immediately following a burn allows active smoke components to settle on the fabric. Repeating the cycle builds a heavy deposit. The 24-hour final stand promotes full chemical interaction and equilibrium between the smoke film and the coating.
⚡ How does the cleaning procedure reflect real-world cleanability? The specified procedure (ethanol wipe, 10-minute wetting, second wipe, rinse) is a standardized, rigorous method to assess the permeability of the coating to smoke stains. It determines whether the discoloration is merely surface deposition or a deeper absorption.
📌 What does a “Heavy” discoloration rating imply for product performance? A “Heavy” or “Very Heavy” rating suggests the coating is highly susceptible to smoke staining. Such a material may require more aggressive cleaning methods or a protective top coating to be viable in indoor environments where smoking occurs.