According to IS 287: 1993, in classifying timber, the average annual relative humidity (%) of Zone IV region of India is more than:
IS 287 and Timber Seasoning
The Indian Standard IS 287: 1993 provides guidelines for the maximum permissible moisture content in timber for various uses. To account for India's diverse climate, it divides the country into four distinct zones based on average annual relative humidity. This zoning helps determine the appropriate level of seasoning required for timber to achieve equilibrium with its surrounding environment, thus preventing defects after installation.
📝 Detailed Analysis of the Options
The question specifically asks for the lower threshold of Zone IV. Let's review the definitions of the zones:
- Zone I: Average annual relative humidity is less than 40%.
- Zone II: Average annual relative humidity is between 40% and 50%.
- Zone III: Average annual relative humidity is between 50% and 67%.
Based on this classification, options (a), (b), and (c) represent thresholds for other zones, not Zone IV.
(d) 67
This is the correct answer. According to IS 287: 1993, Zone IV encompasses the regions with the highest humidity in India. This zone is defined as having an average annual relative humidity of more than 67%. Timber used in these regions, which include coastal areas, requires the most thorough seasoning to reach a stable moisture content.
📊 IS 287: 1993 Timber Seasoning Zones of India
| Zone | Average Annual Relative Humidity (%) |
|---|---|
| Zone I | < 40 |
| Zone II | 40 – 50 |
| Zone III | 50 – 67 |
| Zone IV | > 67 |
💡 Study Tips
- Memorize the Zones: It's helpful to remember the four zones and their humidity ranges, especially the boundary values: 40, 50, and 67.
- Zone IV is the Highest: Associate Zone IV with the most humid regions of India, meaning its threshold will be the highest value, which is >67%.
- Check the Standard: When in doubt, always refer back to the specific Indian Standard code mentioned in the question, in this case, IS 287.