Safety in Thermodynamics Packet

This packet is intended for use in an undergraduate mechanical engineering thermodynamics course, but may be used in other disciplines. The material in this packet should help familiarize students with a few basic safety considerations in thermodynamics. Emphasis is placed on designing with safety in mind, and the six basic guidelines set by the National Safety Council are presented. An example of a water heater explosion in a school is given.

Time for presentation is estimated to be 30 minutes.

Objectives:

1. To introduce students to safety considerations found in thermodynamics.
2. To make students aware of designing with safety as a prevailing concern.
3. To introduce students to the six basic guidelines set by the National Safety Council.

This packet includes the following items:

• Lecture material for the instructor
• Overheads for use during the lecture
• Homework problems and solutions

Download the Thermodynamics Module in printable Adobe Acrobat Format (pdf).  This includes overheads in a ready to use format.

Homework problem solutions, exam problems, and exam solutions are available to qualified recipients. Send an email with request information to Dr. Donald Bloswick.

Safety in Thermodynamics Lecture Outline

  1. ASME Code of Ethics
    1. First Fundamental Canon (OVERHEAD 1)
      1. Engineers shall hold paramount the safety, health and welfare of the public in the performance of their professional duties.
      2. Engineers have a responsibility to create safe environments.


  2. National Safety Council's Six Basic Guidelines For Maximizing Safety
    1. There are six basic guidelines which a designer can apply in order to maximize the safety level of his/her products or manufacturing processes.
    2. The National Safety Council has published this list in descending order of effectiveness, such that the highest possible guideline should be used.
    3. The guidelines are: (OVERHEAD 2)
      1. Eliminate the hazard from the product or process by altering its design, material, usage, or maintenance method.
      2. Control the hazard by capturing, enclosing, or guarding it at its source.
      3. Train personnel to be aware of the hazard and to follow safe procedures to avoid it.
      4. Provide adequate warnings and instructions in appropriate forms and locations.
      5. Anticipate common areas and methods of abuse and take steps to eliminate or minimize the consequences associated with such actions.
      6. Provide personal protective equipment to shield personnel against the hazard.
    4. These six rules are interrelated and more than one can be used in a specific situation. For example, machine guarding can be supplemented by training, warnings, and the use of personal protective equipment.


  3. Example: Water Heater Explosion in School
    1. An example of the destruction that can be caused by thermodynamic systems is given in the assignment handouts.
    2. Water heaters, as well as many other appliances, can be deadly when not used appropriately.

Overhead 1

ASME Code of EthicsFirst Fundamental Canon

Engineers shall hold paramount the safety, health and welfare of the public in the performance of their professional duties.

Overhead 2

National Safety Council's Six Basic Guidelines for Maximizing Safety in Design(Listed in descending order of effectiveness)

1. Eliminate the hazard. 2. Control the hazard. 3. Train personnel. 4. Provide adequate warnings. 5. Eliminate or minimize the consequences. 6. Provide personal protective equipment.

Safety in Thermodynamics Assignment

Read the handout, "Water Heater Explosion in School" and answer the following questions:

1. Why was the temperature sensor disabled?

2. What was the equivalent force of the 85 gallon water heater explosion?

3. Why is a pressure only relief valve an insufficient safety device?

4. Rank, in descending order (most to least effective), the best prevention methods for this accident.

a. Regular safety inspections

b. Design better relief valve

c. Posted safety instructions and warnings on water heater.d. Routine safety training for maintenance personnel.

5. Briefly suggest how you could design a better safety valve (or component) that would help prevent this type of accident.

Quantitative Problem:

The development of the ASME pressure vessel code, which requires that tanks be able to withstand four times their operating pressures, dramatically reduced the number of boiler and heater explosions. However, accidents still happen when pressure relief valves and thermostats fail. When a tank filled with high-pressure and high-temperature liquid ruptures, there is a sudden drop in pressure to atmospheric level. This drop creates a large rise in volume and a pressure wave results that can cause considerable damage.

Since the pressurized liquid in the tank quickly reaches equilibrium with the surroundings, the explosive energy of the pressurized liquid can be defined as the work that a pressurized liquid would do if it were allowed to expand reversibly and adiabatically to the pressure of the surroundings.

Consider an 85-gallon hot-water tank that has a working pressure of 1.0 MPa, such as the one in the example. As a result of a disabled temperature sensor, the pressure in the tank rises to 4 times the working pressure, at which point the water heater explodes. Using atmospheric pressure equal to 100 kPa and assuming the liquid to be saturated at the time of the explosion, determine the total explosive energy of the tank.