Regulations Affecting Mercury and Mercury Filled Transducers
The Government classifies mercury as a hazardous material and as such, there are a number of laws and regulations covering its use and handling. Mercury can be found in a number of electrical switches, relays, manometers and transducers.
Regulations in the work place are covered by the U.S. Department of Labors Occupational Safety and Health Administration (OSHA). Under OSHA, companies using mercury and products containing mercury are required to post a Material Safety Data Sheet containing:
1. The product name, manufacturer, emergency phone number.
2. Description of the hazardous material and regulations involved.
3. Physical and Chemical Characteristics.
4. Fire and Explosion Hazard Data.
5. Reactivity Data
6. Health Hazard Data
7. Precautions for Safe Handling.
8. Control Measures.
The dangers from mercury and mercury vapor, include acute and chronic mercury poisoning, symptomized by inflammation of mouth and gums, loosening of teeth, impaired digestion and kidney/liver functions, tightness of chest, chest pain, difficult breathing, mental problems, such as memory loss and erratic motor function. Exposure to mercury vapor naturally accelerates the dangers.
Manufacturers of mercury products are required to comply with OSHA 29 CFR 1910.1200 by supplying Material Safety Data (MSD) sheets to customers, who in turn, are required to post them conspicuously in the work place under the "Right to Know Act".
The transportation of mercury and mercury devices is covered by hazardous materials regulations under the Department of Transportation (DOT) and International Air Transport Association (IATA) requiring special handling procedures by freight carriers. These procedures require a hazardous material warning label for all air shipments regardless of the amount of mercury, and for land freight in amounts of 1 pound or more. The freight carriers naturally charge a special handling fee for such hazardous materials, which can amount to $10.00 to $65.00 plus regular freight cost. These shipping costs are chargeable to the customer.
The disposal of split mercury or mercury containing plastic is covered under EPA regulations, and in no case is it legal to dispose of it in regular trash or trash collections. Regulations call for packing in an airtight metal container for storage and shipment as a hazardous waste to a certified/licensed hazardous waste disposal from who will dispose of it in the prescribed manner. Depending on the amount and the disposal firm, the cost for disposal can amount to several hundred dollars. Sometimes, manufacturers take their materials back at a cost somewhat less than disposal firms charge and dispose of larger quantities at better rates. Companies that dispose of mercury improperly are subject to fines.
Plastic Melt Transducers containing mercury are not exempt from the foregoing regulations and commonly are subject to breakage by abusive handling and by polymer cooling and sucking off the 0.0045" stainless foil disk separating the mercury from the product. Any mercury escaping into the molten plastic or leaking onto a hot metal surface can vaporize or partially vaporize into most toxic gaseous form. Mercury filled transducers have been known to operate without failure for periods of time ranging from hours, days and weeks to several years, depending on their quality and condition of usage. Manufacturers are not able to guarantee how long they will last.
Not all manufacturers of mercury filled devices, instruments and sensors comply with the foregoing regulations, putting their customers at considerable risk of violation of OSHA, EPA and shipping regulations. Examples of companies that comply with mercury regulations are attached.
Melt Pressure
Transducers Comparisons
| Parameter | Liquid-Fill | Push-Rod | Silicon Sapphire |
| Thickness | 0.0045 | 0.005-0.010 | 0.022-0.040 |
| Thickness Ratio | 1 | 1.1 - 2.2 | 5-9 |
| Material | Stainless | Stainless | Silicon on Sapphire |
| Hardness Ratio | 1 | 1 | 50 |
| Abrasion Resistance-fiberglass | Poor | Fair | Excellent |
| Fatigue Resistance | Fair | Fair to Poor | Excellent |
| Shock & Vibration Resistance | Good | Good | Excellent |
| Hysteresis | Yes | Yes | Virtually None |
| Response Time, mV | 30 30 millisec | 30 millisec | < 100 Micro-Sec |
| Response Time, 4-20 mA | 100 30 millisec | 100 millisec | < 1 Milli-Sec |
| Accuracy, % FSO | .5 & 1% | Mostly 1% | .5 & 1% |
| Temp Sensor in Diaphragm | No | No | Optional RTD on diaphragm |
| J-TC in Threaded Shank | Optional | Optional | Optional |
| Accuracy of Melt Temp Sensor | None | None | +/- 0.5o |
BODY
| Body Material | Stainless | Stainless | Stainless |
| Optional Lengths | Yes | Yes | Yes |
Connector
| Material | Aluminum | Aluminum | Stainless |
| Insulation Max Temp Rating | 200F | 200F | 600F |
Transducer
| Type | Bonded Foil Strain Gage | Bonded Foil Strain Gage | Piezo Resistive Strain Gage |
| Location-Strain Gage | Remote | Remote | Diaphragm |
| Heat Resistance-Strain Gage | 250F | 250F | 750F |
| Heat Resistance-Diaphragm | 750F | 750F | 750F |
| Fill Material | Mercury*NaK | Push-Rod* | None |
| Fill Classification | Hazardous* | Non-Hazardous | Non-Hazardous |
| OK in Food Packaging | No* | Yes | Yes |
| OK in Medical Products | No* | Yes | Yes |