A 55-gallon drum is a widely used container for storing and transporting liquids and materials. Understanding its pressure capacity is a fundamental safety concern, directly impacting workplace safety and environmental protection. Recognizing the factors that influence a drum’s pressure limits and the potential hazards of exceeding them is important for anyone handling or storing them.
Drum Construction and Types
The pressure resistance of a 55-gallon drum is determined by its construction materials and design. Common drums are manufactured from steel, including carbon steel, stainless steel, and galvanized steel, or from plastics like high-density polyethylene (HDPE) and polyvinyl chloride (PVC). Steel drums are recognized for their strength and durability, often featuring wall thicknesses between 0.9 and 1.5 millimeters (approximately 20 to 16 gauge), with reinforced ribs or rolling hoops adding to their structural integrity.
Plastic drums, while lighter and resistant to corrosion and certain chemicals, typically have a minimum wall thickness ranging from 2.2 to 2.3 millimeters (around 0.087 to 0.090 inches), and sometimes up to 3-5 millimeters. Beyond material, the drum’s design, specifically whether it is an open-head or closed-head (tight-head) type, plays a role in its pressure capability. Closed-head drums have permanently sealed tops with small bung openings for filling and dispensing, making them suitable for liquids and offering greater integrity against internal pressure, while open-head drums feature removable lids secured by a locking ring, primarily used for solids or viscous materials.
Factors Affecting Pressure Capacity
Several external and internal factors can significantly alter a 55-gallon drum’s pressure capacity beyond its initial design specifications. Temperature fluctuations are a primary concern, as increasing temperatures cause both the drum material and its contents to expand. This expansion directly increases internal pressure, a phenomenon particularly pronounced with volatile liquids, which generate higher vapor pressures when heated. Conversely, rapid cooling can create a vacuum, potentially leading to drum collapse.
The nature of the drum’s contents also plays a significant role. Materials that are volatile, generate gases through chemical reactions, or undergo biological activity (such as fermentation or decomposition) can lead to a buildup of internal pressure. The age of a drum, along with wear or physical damage like dents or corrosion, compromises its structural integrity. Moving a sealed drum from a lower to a higher altitude can also induce a modest increase in internal pressure due to changes in atmospheric conditions.
Understanding Pressure Limits and Hazards
The pressure a 55-gallon drum can withstand varies considerably between types and conditions. Standard steel drums are designed to contain pressures up to 5 to 7 pounds per square inch (psi) before requiring a pressure relief mechanism. Some steel drums are tested to withstand hydrostatic pressures ranging from 150 kilopascals (approximately 21.75 psi) to 250 kilopascals (approximately 36.25 psi) during UN performance certification.
While burst pressures for 55-gallon metal drums can be as low as 14 psi, they might hold up to 30 psi, with closed-top drums typically failing below 48 psi. Plastic drums exhibit a lower pressure tolerance compared to steel drums. They may begin to bulge at around 30 psi, and a pressure difference of approximately 14 psi between the inside and outside can lead to failure.
Exceeding these limits can lead to drum rupture, uncontrolled release of hazardous contents, or even an explosion. A small pressure increase, such as 2 psi in an open-top drum, can create an upward force of about 760 pounds on the lid, potentially turning it into a dangerous projectile. Manufacturers produce drums to specific safety standards, such as those set by the Department of Transportation (DOT) and the United Nations (UN), which mandate rigorous testing including drop tests, leakproofness, hydrostatic pressure, and stacking tests to ensure safe transport of materials.
Safe Handling and Prevention
To prevent over-pressurization and ensure safe handling of 55-gallon drums, several practices are important. Installing pressure relief vents is important, as these devices automatically release internal pressure, typically between 3 and 8 psi (30 to 55 kPa), and can also prevent vacuum formation during dispensing. These vents are particularly important for drums containing volatile liquids or materials that might generate gas.
Storing drums in a controlled temperature environment and away from direct sunlight helps prevent internal pressure buildup caused by thermal expansion of contents and drum materials. Avoid mixing incompatible chemicals within a drum, as this can lead to reactions that produce gases and increase pressure. Regular inspection of drums for physical damage, corrosion, or compromised seals is important to identify weaknesses before they lead to failure.
Adhering to manufacturers’ guidelines and regulatory requirements, such as UN/DOT standards, is important for safe operation. Fifty-five-gallon drums are designed for storage and transport of liquids at atmospheric or low pressures, not for highly pressurized gases or high-pressure applications.