Exposure to Mercury Vapor During the Use of

Mercury Car bu re tor Syn chro nizers

 De scrip tion of HAZARD 

In mo tor cy cle and ma rine out board en gines with mul ti ple car bu re tors, the vac uum pres sure of each car bu retor should be bal anced. Me chanics com monly use mer cury car bu re tor syn chro niz ers for this pro ce dure. Ex -

po sure to mer cury may oc cur in two ways. Mer cury car bu re tor syn chro niz ers (gauges) con tain about

40 grams of mer cury that can be spilled if these gauges are not han dled or stored prop erly. Also, im proper

en gine tun ing can cause mer cury to be sucked into the en gine and re leased in stantly in high con cen tra tions

from the ex haust sys tem. Acute ex po sure to high con cen tra tions of mer cury va por can af fect lung func tion

and pos si bly dam age the lungs. Mer cury can also en ter the body through the skin. Pro longed ex po sure to

mer cury can dam age the kid neys and the cen tral ner vous sys tem.

The Na tional In sti tute for Oc cu pa tional Safety and Health (NIOSH) is also con cerned that many mo tor cy cle

and ma rine me chan ics work in ga rages with out ef fec tive ven ti la tion sys tems for con trolling mo tor ve hi cle

emis sions. To re duce ex po sure to these emis sions, the me chan ics rely on nat u ral ven ti lation from open

doors and win dows, or they try to limit the amount of time an en gine runs in side the ga rage.

 Recommendations for Prevention

O Ven ti la tion

Mo tor cy cle ser vice ga rages should be equipped with an en gine ex haust ven ti la tion sys tem to con trol car bon

mon ox ide and other con tam i nants. Also re ferred to as “ex haust col lec tors,” these fan-powered sys tems are

placed ei ther over head or un der the floor, and are con nected to flex i ble ducts that the me chanic at ta ches to

the ve hi cle tail pipes. Ma rine me chan ics should tune out board mo tors in wa ter tanks equipped with a slot exhaust ven ti la tion sys tem placed at the rear of the tank. Draw ings and de sign spec i fi ca tions for these ven ti lation sys tems are avail able from the Amer i can Con fer ence of Gov ern men tal In dus trial Hy gien ists,

Cincinnati, Ohio.

O Work Prac tices

1. Read the manufacturer’s instructions carefully before loading or using the mercury carburetor

synchronizer. The gauges are shipped empty and must be loaded with mercury by the user. Make sure

the top of the gauge is elevated about 1 inch before filling the mercury reservoir. Otherwise, the

mercury will spill out of the top of the tubes.

HAZARD ID

HID 6
2. Adjust the carburetors only while the engine is idling at 1,000 rpm. After the carburetors are synchronized

at 1,000 rpm, the tuning procedure requires that the engine speed be slowly raised to 3,000 rpm to see

whether the carburetors remain synchronized. Engine speeds exceeding 3,500 rpm can cause mercury

to be drawn into the engine. Rapid throttle movements— especially cutting the throttle during a high

engine speed— can also cause mercury to be sucked into the engine.

3. Evacuate the area immediately if mercury is drawn into an engine that is not connected to a properly

functioning exhaust collector. It is likely that high concentrations of mercury vapor would be released

instantly from the exhaust. Dissipation of these vapors would depend on the amount of ventilation

supplied to the garage.

4. To avoid leaks, store the synchronizer in an upright position with the reservoir vent-cap closed.

5. Spills provide a continuous source of exposure to mercury vapor until the spill is cleaned up. If mercury 

is spilled, restrict access to minimize tracking mercury to other areas; ventilate the area by opening

windows. Immediately contact your State health department or the U.S. Environmental Protection

Agency (EPA) for detailed advice about the proper procedures for cleaning up and disposing of spilled

mercury.

O Sub sti tu tion

Two types of mer cury-free in stru ments are avail able for syn chro niz ing car bu re tors: an a log gauges (also

known as vac uum gauges) and elec tronic gauges. Both of these are more ex pen sive than mer cury gauges,

which cost $30 to $50. Vac uum gauges cost about $100, and elec tronic gauges cost $330. How ever, the

proper cleanup and dis posal of spills from mer cury gauges can be ex pen sive. The EPA re quires that mer cury

from non res i den tial spills be treated as haz ard ous waste by a li censed waste dis posal com pany.

 For More Information

To ob tain more free in for ma tion about con trol ling this haz ard, or to ob tain in for ma tion about other oc cu pational safety and health is sues:

 Acknowledgments

The prin ci pal con tri bu tors to this pub li ca tion were Ste ven A. Lee, CIH, and Jerome Flesch, MS, of NIOSH;

and Lyle E. McKenzie of the Col o rado De part ment of Health. Desk top pub lish ing was pro vided by Kristina

Dragon and Su san Kaelin.

June 1999 DHHS (NIOSH) Publication No. 99–111

— call NIOSH at 1–800–35–NIOSH (1–800–356–4674), or

— visit the NIOSH Homepage on the World Wide Web at

http://www.cdc.gov/niosh

U.S. DEPARTMENT OF HEALTH AND HUMAN SERVICES

Public Health Service

Centers for Disease Control and Prevention

National Institute for Occupational Safety and Health

CDC CENTERS FOR DISEASE CONTROL

AND PREVENTION