Overfill / Spill Prevention in Solvent Tanks

Solvent storage is common in many industries including paint and coating manufacturing, plastics, pharmaceutical, and cosmetics.

Spills of solvents have far-reaching repercussions including clean-up cost, down time, loss of material, HSE / EA fines, and potential injury to facility personnel. If the spill is due to negligence on the part of the facility management, responsible parties may even receive a custodial sentence.

Preventing a single spill by installing a high level spill prevention alarm will pay for itself many times over.

What is an Overfill / Spill Prevention Alarm?

Switches used to prevent spills are installed in a vessel to warn an operator when material reaches a dangerously high point. As such, these switches can go for months or even years without seeing material. It is imperative that the switch functions during an actual high level event. For this reason, any high level device used for spill prevention must have a feature that reliably tests the function of the switch to ensure it will operate properly in an actual high level condition.

High-level switches used for overfill/spill prevention are not intended to be used as “stop fill” indication devices. Customers will sometimes try to utilise their continuous tank gauging measurement, with integral high-level control point, for overfill/spill prevention in an effort to reduce costs. Relying on the tank-gauging device for spill prevention is a risky practice.

Considering the low price of an independent point level switch and the insurance it provides, the justification is simple. Also, the UK’s Fire Protection Association states in NFPA 30* “Flammable and Combustible Liquid Code” that high level detection devices used for overfill prevention must be independent of the tank gauging level device.

Spill Prevention Technologies

The following is a review of the most common point level measurement devices used for spill prevention.

Float Switch

Floats are commonly used for overfill alarm indicators because they are low priced, however, floats are a poor choice for preventing spills. The float can jam or hang up preventing the switch from alarming in a high level condition. The float can also leak causing it to fail. The only way to test for these failures is to raise the material level to see if the switch will work. Raising the material level for a test is not the most prudent course of action when your spill prevention alarm may or may not work.

Tuning Fork

Tuning forks have become popular for overfill protection in recent years mainly because they require no calibration. Some tuning forks are available with test features that indicate if the forks have corroded or if the piezoelectric crystals have failed, however, forks are easily damaged making this technology an unreliable choice for spill prevention. Other technologies such as RF Admittance are much more robust and better suited to industrial installations.

Ultrasonic Gap Switches

Gap switches require no calibration and have no moving parts, reducing maintenance needs. Gap switches such as the VeriGAP from Drexelbrook, are available with manual and/or self-test features that ensure proper operation. There are high temperature limitations on the use of the gap switch (typically 350o F) and applications where the material may coat or clog the gap. Where the application is appropriate, VeriGAP switches are a good choice for overfill/spill prevention.

RF Admittance

Drexelbrook RF Admittance Intellipoint incorporates a self-test feature that checks the integrity of the entire point level switch three times a second. A manual Certify test button allows the operator to check the entire control loop, including the sensor, measuring circuit, relays, and the annunciator or interlock device. There are no moving parts to wear or jam and the sensors are robust, designed for long life and minimal maintenance.

The Intellipoint calibrates itself. Simply install the sensor in the vessel and apply power. The Intellipoint combines the most reliable technology with the features needed to ensure you will never overfill your vessel again.

The Drexelbrook Intellipoint is the clearly the best choice for overfill/spill prevention given the critical nature of the application. A MTTF (Mean Time To Fail) of 110 years makes the Intellipoint unrivalled in performance and reliability.

For more information regarding this article, please contact ABLE Instruments on +44 (0)118 9311188 or by email: info@able.co.uk.

*The FPA have a formalised relationship to use the National Fire Protection (NFPA) codes and standards.