When installing underground tanks, several safety measures must be followed to prevent structural damage, leaks, and other hazards. Here's a breakdown of key requirements:

1. Location: Exercise caution during excavation to avoid undermining existing foundations 2, 3. Position underground tanks so that the loads from building foundations and supports are not transmitted to the tank 1, 2, 3. Maintain specific distances from basements, pits, and property lines, depending on the category of flammable liquid stored 1, 2, 3.
2. Depth and Cover: Place underground tanks on firm foundations and surround them with at least 6 inches of noncorrosive, inert materials like clean sand or gravel, well-tamped in place 1, 3, 11. Handle tanks carefully during placement to avoid damage 1, 3, 11. Cover tanks with a minimum of 2 feet of earth, or 1 foot of earth plus a 4-inch thick reinforced concrete slab 1, 3, 11. In areas subject to traffic, increase the protection to 3 feet of earth cover, or 18 inches of well-tamped earth plus reinforced or asphaltic concrete 1, 3, 11. Paving should extend at least one foot horizontally beyond the tank's outline 1, 3, 11.
3. Corrosion Protection: Implement corrosion protection for both the tank and its piping through methods like protective coatings/wrappings, cathodic protection, or corrosion-resistant materials 3, 11.
4. Vents: For Category 1 or 2 flammable liquids, or Category 3 flammable liquids with a flashpoint below 100°F (37.8°C), ensure vent pipes are located outside buildings, higher than the fill pipe opening, and at least 12 feet above ground level 3, 11. Vent pipes should discharge upwards to disperse vapors and avoid obstructions that could cause excessive back pressure 3, 11.
5. Tank Openings: All tank openings must have vapor or liquid-tight connections [1]. Provide openings for manual gauging with liquid-tight caps or covers [1]. Fill and discharge lines should enter tanks through the top and fill lines should slope towards the tank [1].
6. Flood Protection: In flood-prone areas, take precautions such as not locating tanks below the maximum flood stage, providing independent water supply facilities, and safeguarding tanks against movement when empty or submerged 4, 6, 10, 14. Anchor, weight, or secure tanks to prevent movement during flooding 4, 6, 10, 14.
7. Piping: Provide pipe connections below the liquid level with valves or cocks located close to the tank shell, made of steel or suitable material 6, 10, 14.
8. Materials and Construction: Tanks must be built of steel or other approved materials suitable for the stored liquid [2]. Non-steel tanks must adhere to engineering design principles [2].
9. Filling Connections: Locate filling and emptying connections outside of buildings, away from ignition sources and building openings. Ensure connections are closed and liquid-tight when not in use and properly identified 1, 2, 3.
10. Static Electricity: For certain flammable liquids, design and install fill pipes to minimize static electricity generation 1, 2, 3.

By adhering to these guidelines, you can significantly enhance the safety of underground tank installations.