Which method is ineffective for ice removal on sight glasses?

The method identified as ineffective for ice removal on sight glasses is the use of physical scraping. This approach can potentially damage the sight glass material, which is typically made of glass or a similar transparent polymer. Scraping can lead to scratches or cracks that compromise the integrity of the sight glass, making it unsafe for use, as it may lead to leaks or visibility issues.

In contrast, the other methods listed are more suitable. Alcohol spray can lower the freezing point of water and assist in melting ice without causing damage. Heat generation, such as using a heat gun or warm cloth, can effectively melt ice while being gentle on the glass. Compressed air blasts can remove loose ice and frost without contact, reducing the risk of damage entirely. Thus, the physical scraping method is not only ineffective in safely removing ice but can also lead to further complications with the equipment.