Sometimes, some auditors behave like this. They do not think about the issue in a holistic way. Somehow, they tend to show their authority and misuse the whole concept. In all our day-to-day activities, we come across many such issues. As Dipil rightly said, one has to use the most practical solution.
If sand is hazardous, what is the alternative? Fire extinguishers? Is using chemicals not hazardous? Practically, once the fire is extinguished by whatever means, the remains are collected and disposed of safely.
Next time such impractical suggestions are given by the auditor, suggest to them to use a bicycle to come to your place instead of a car/bike/scooter, which pollutes the air.
Regards,
Nandish