Detailed air monitoring was conducted by Holland
and Dr. Mark Van Art of the School of Health Related Professions, University of
Arizona on June 4, and June 13, 1985. On the first day of monitoring, a museum worker
handled nitrate negatives exclusively. On the second sampling day, only diacetate
negatives were handled. Seven air samples were collected on each day. Sampled locations
included the worker's breathing zone, the immediate desk work area and the general
workroom area.
After completing the second day of sampling, it was noticed that upon peeling
the emulsion away from the backing of a discarded diacetate negative, a strong organic
odor was immediately evident as well as some dampness between these layers. Dr.
Van Ert suggested that the diacetate negatives were off-gassing acetic acid. Several
diacetate negatives were peeled and sealed in a flask to contain any vapors being
released. After three days, an air sample was collected from inside the flask using
large SKKC charcoal tubes and analyzed using gas chromatography/mass spectroscopy
to identify all organic compounds present. The result of this test indicated acetone
and mesityl oxide in a relative ratio of approximately five to one. Based upon this
information, the air samples collected on June 4 and 13 were split, analyzing two
for mesityl oxide and acetone while the remainder was analyzed for acetic acid.
Acetone
According to Nelson and Web (1978) acetone can be placed among solvents of comparatively
low acute and chronic toxicity. High vapor concentrations may be irritating to the
eyes, nose and throat, and may produce anesthesia. Eye; contact with acetone is
especially hazardous and may cause blindness (Shaw, 1983:3.262). The odor may also
be disagreeable. There have been no confirmed reports that prolonged inhalation
of low vapor concentrations result in any serious chronic effects in humans.
The museum samples analyzed for acetone were collected approximately 1-1/2 ft.
from the breathing zone. Acetone levels measured less than 0.2 mg/M3.
The OSHA standard for acetone is 2400 mg/M3. The
1986 TLV accepted by industry for the normal 8-hour day is 1780 mg/M3
or 750 ppm acetone. Respiratory protection should be used at higher levels (Nelson
& Web, 1978).
Mesityl oxide
Mesityl oxide is a derivative of acetone and is used as a glue base in the making
of plastics, acetates, and films. It is also used as a solvent in gums, resins (particularly
vinyl resins), lacquers, varnishes, enamels, and nitrocellulose.
The hazards of mesityl oxide include flammability and moderate fire risk (curators
are well aware of the flammability of decomposing nitrate negatives). This solvent
may become free as the molecular structure of film breaks down with age (Nancy Odegaard,
1985). Mesityl oxide can affect the skin, eyes, respiratory system and central nervous
system. Symptoms of exposure are irritated eyes, skin irritation, irritation of
the mucous membrane, vertigo, and in extremes cases of overexposure, coma.
The samples analyzed for mesityl oxide were collected approximately 1 1/2 ft
from the breathing zone of the museum worker handling the negatives. Mesityl oxide
levels measured less than 0.4 mg/M3. OSHA standard
for mesityl oxide is 100 mg/M3 with 1986 TLV of 60 mg/M3.
Acetic acid
Diacetate negatives release acetic acid in addition to nitrogen oxides. Acetic
acid, like nitric acid, is an irritating and corrosive material. Mucous membranes
are particularly susceptible to contact with this acid due to the hydrated nature
of their surfaces. Acetic acid has been shown to be corrosive to the epithelial
layer of the cornea and may induce permanent ocular granules. Pulmonary response
to acetic acid mist is typical of exposure to a reactive upper-respiratory tract
irritant. It produces increased resistance to airflow due to bronchial constriction
and subsequent decrease in breathing frequency.
Acetic acid concentration among project materials were first measured by cutting
several diacetate negatives and placing cut section in a sealed 500mL Erlenmeyer
flask for 24 hours. A concentration of 60 ppm of acetic acid was detected in the
flask using Bendix/Gastec indication tubes. However, filter samples tested from
both personal breathing zone and work area demonstrated non-detectable concentration
of acetic acid, less than 2 mg/M3. The OSHA standard
for acetic acid is 25 mg/M3. The 1986 TLV for the
same materials is 25 mg/M3.
Although conventional air monitoring techniques at ASM to date have shown minimal
levels of contaminants in the breathing zone of museum workers, the symptoms experience
by the workers are significant enough to strongly indicate the presence of an offending
air contaminant or combination of contaminants. The compounds that have been identified
as being present are nitrogen dioxide, acetone, mesityl oxide, and acetic acid.
Even at very low concentrations, synergistic effects may occur where to or more
compounds act together to aggravated a symptom. The possibility exists that theses
contaminants may bind to fine particulates generated during the handling of negatives,
which would enhance their potential for irritation and penetration to the lower
respiratory tract. |
