Step 1: Understanding the Concept:
For first order, $k = \frac{2.303}{t} \log \frac{a}{a-x}$.
Step 2: Detailed Explanation:
For $99%$, $k = \frac{2.303}{32} \log 100 = \frac{2.303 \times 2}{32}$. For $99.9%$, $t = \frac{2.303}{k} \log 1000 = \frac{2.303}{k} \times 3 = 32 \times \frac{3}{2} = 48$ min.
Step 3: Final Answer:
Time required is $48$ min.