| Face piece respirators
In some work environments where exhaust ventilation is infeasible or air contaminants
cannot be adequately contained by a hood or other means, respirators may be considered
for providing protection for personnel.
Unfortunately, respirators are frequently purchased without enough information
to make a proper selection. Respirators either filter (air purifying respirators)
or supply breathing air; the former type is appropriate to our discussion. The most
important consideration in buying respirators, however, should be whether anyone
is really going to wear them. Even the best-designed respirators are very uncomfortable
to wear even for a few hours. If the devices are being employed only to filter an
odor or slight irritant, many employees will eventually elect to tolerate the contaminants
rather than wear the respirator In addition, if an employer requires an employee
to wear a respirator as part of the job, then a detailed physical is required under
OSHA to verify that the worker is physically capable of breathing through a respirator.
If it is determined that air purifying respirators are required in a given situation,
then selection should be governed by several criteria. The first criterion is the
type of filtration needed. If air contaminants to be encountered are all particulates
such as silica or asbestos, then the respirator to be purchased should be approved
for use with these materials. If a solvent such as nitrocellulose is to be handled,
than an organic vapor respirator would be recommended. The second criteria should
be comfort. Respirators are made out of paper, plastic, neoprene, or silicone materials
depending on the application. Some of the materials may be more irritating to the
wearer then the contaminants they are trying to control. The third criterion is
cost. Some models are disposable, others are not, requiring periodic maintenance
and part replacement. NIOSH/MSHA approved disposable organic vapor /acid gas respirators
can be purchased at an average cost of $13.oo. NIOSH/MSHA respirators using replaceable
filters for organic vapors/gases are more expensive at $287.50 with additional filter
costs. In any event, respirators should be chosen with care and forethought.
Eye Protection
Goggles may be problematic when worn under poor ventilation condition in the
presence e of nitrate and diacetate negatives. Gases may concentrate inside goggles
and cause additional eye irritation. Nitrogen oxides, Mesityl oxide, and acid vapor
in particularly can be extremely irritating to the eye. Proper ventilation is be
far the best protection from these eye-irritating gases, and reduces or eliminates
the need for equipment such as goggles.
Contact lenses should not be worn in the presence of deteriorating negatives
for extended periods of time. Nitrogen oxides, mesityl oxide, and airborne acids
may concentrate beneath contact lenses and cause added injury to the eye. These
gases and acids will specifically contaminate some lenses, rendering them unfit
for future use. Handlers of aging negatives should consider this potential problem
with contact lenses and entertain the possibility of wearing glasses. Again, appropriate
ventilation will eliminate such a problem.
Gloves
Wear vinyl or latex gloves while working with decomposing negatives to limit
skin irritation. Cotton gloves can be worn over the latex gloves if preferred for
handling delicate films. Long sleeves are recommended to prevent the glove top from
making direct contact with the wrist; perspiration at this site could allow contaminants
to concentrate on the skin. At all times, workers refrain from cross contaminating
the sensitive areas of the eyes, nose, mouth and neck.
Limit handling and exposure time
While appropriate ventilation control measures are being effected to reduce exposure
to emission products of negatives, the recommended handling time for deteriorating
negatives is 2-3 hours per day, or per session if separated by lengthy non-exposure
periods. Actual time will depend upon the worker's capacity to deal with the materials.
Handlers might find that they are more comfortable limiting their exposure to 1
or 1 1/2 hours in a darkroom where there is a possibility of various interactions
involving the negatives and other darkroom chemistry. Ideally effective ventilation
should eliminate the need for limited work time.
Clean work surfaces
After work sessions, surfaces should be cleaned with a solution of baking soda
and water (about 1 teaspoon per pint, or 16g sodium bicarbonate to 1 liter of water).
This mild wash of sodium bicarbonate will neutralize acids left behind when aging
nitrate or diacetate negatives are cleared away.
Monitor temperature and humidity
Nitrate film base decomposes slowly under ordinary conditions and the rate of
decomposition is accelerated by k creasing relative humidity and temperature (Eastman
Kodak, 1979). Relative humidity must not exceed 60% in storage for nitrate negatives,
with 35-40% recommended (Hendriks, 1984:84). Relative humidity should not be allowed
to fall below 20% or the film base may become too brittle (Kodak Publication No.
F-30, 1979).
The rate of decomposition of films on cellulose nitrate bases approximately
doubles with each 6o C (11oF) increase in temperature. A constant storage temperature
10oC (50o) is preferable for the storage of nitrate and diacetate negatives (Eastman
Kodak, 197779). Temperature in storage should not rise above 21oC (70oF) at any
time. Fluctuating temperature and humidity adds to the instability of the object,
and will promote chemical degradation, so do not allow cycling of relative humidity,
or fluctuations in temperature greater than 4oC (Hendriks, 1984:85).
Low temperatures provide added protection. Processed photo materials can be
kept below the freezing point (0oC, 32oF) provided rH is at constant acceptable
levels (Hendriks, 1984:85). Freezing (rH 45% and temperature of -18oC, 0oF) has
been used successfully at the University of Ann Arbor. Materials removed for further
preservation are allowed to adjust to normal room temperatures for 4 days (Eaton,
1985:93).3
A fine source for monitoring procedures and equipment can be found in Ritzenthaler,
1983 (pages 32-34). A carefully monitored environment will help to assure continuing
safety for materials and staff.
Avoid vapor accumulation in storage
Care should be taken that gases are not allowed to accumulate in the work or
storage environment. Nitrate films should be stored apart from other negatives and
prints in a cool place with sufficient ventilation to exhaust the toxic gases produced
by the decomposition of nitrocellulose (Shaw, 1983:293). Presently isolated cold
storage as described above is considered best suited for extending the life of a
nitrate negative. However, some institutions may not have cold storage facilities
at their disposal. In such cases, adjustments to cabinetry can assist in diminishing
accumulation of problem vapors.
Storage of aging nitrate and diacetate negatives in acid free paper products
as generally recommended is suitable (Ritzenthaler, 1983; Hendriks, 1984). It is
not recommended that deteriorating negatives be stored within boxes or cabinets
shared by other record materials, such as tin-types, paper prints, or objects composed
of leather (Eastman Kodak, 1979; Time-Life Books, 1982; Shaw, 1983; Eaton, 1985;
Nancy Odegaard, 1987). Over long periods of time, confined corrosive acid vapors
can damage these objects.
To accomplish a dual goal of ventilating the collection while still affording
a sufficient degree of archival protection, a closed cabinet with a constant flow
of air through its interior would be an effective solution.
The ideal installation provides airflow into vents in the cabinet by generating
negative pressure through an exhaust system. The mount of air exhausted through
a cabinet does not need to be very large. A typical restroom exhaust fan that exhausts
50 CFM should be adequate for most large cabinets used in this type of application.
The fan can be installed to exhaust through a fume hood, window, ceiling, or other
building exhaust duct, and connected to the cabinet with flexible duct such as that
commonly used on dryer vents. The exhaust opening in the cabinet should e as far
as possible from the air inlet opening to maximize the dilution effect of fresh
air flowing through the cabinet. The best arrangement would have the exhaust outlet
near the back and top of the cabinet, with filtered air inlet louvers near the bottom
of the cabinet front. This will allow air entering the cabinet to flow over the
collection, carrying contaminants to the exhaust as they are generated during storage.
The room air being exhausted through the cabinet must be of adequate quality in
terms of temperature and humidity to avoid damaging the collection. Should adjustments
to cabinetry be impractical, be sure that the storage drawers are routinely opened
each three to for weeks to dissipate gas accumulation. Don't bend to work over deteriorating
photo materials that have been in closed storage for months or years. |
