Data Useful for Health
Identification (MSDS)
• Threshold Limit Values
(TLV)
• Odor threshold for vapor
• Physical state
• Vapor pressure of liquid
• Sensitivity to chemical or
impact
• Rates and heats of reaction
• Hazardous by-products
• Reactivity with other
chemicals
• LEL and UEL
• Noise level of equipment
• Types and degree of
radiation
MSDS at ITRI
http://www.iosh.gov.tw/msds.htm
Evaluation
The evaluation phase determines the extent and
degree of employee exposure to toxicants and
physical hazards in the workplace environment.
To establish the effectiveness of existing controls,
samples are taken to determine the worker’s
exposure to conditions that may be harmful.
After obtaining the exposure data, it is
necessary to compare them with standards
such as TLVs, PELs and IDLHs.
Evaluating Exposures to
Volatile Toxicants (1)
For continuous concentration data, the timeweighted average concentration (TWA) is
1 tw
TWA   C (t )dt
8 0
where C(t) is the measured concentration in
ppm or mg/m^3 of the chemical in air and
tw is the worker shift time in hours.
Evaluating Exposures to
Volatile Toxicants (2)
For intermittent samples obtained at fixed
points in time
n
CiTi

TWA  i 1
8
where Ci is the measured concentration value
in the ith period of time Ti.
Evaluating Exposures to
Volatile Toxicants (3)
If more than one chemical is present in the
workplace, one approach is to assume that
the effects of toxicants
are
additive.
Let
n
Ci
A
i 1 (TLV  TWA ) i
where Ci is the concentration of chemical i; n
is the total number of toxicants; (TLVTWA)i is the TLV-TWA for chemical i. If A
exceeds unity, then the workers are overexposed.
Evaluating Exposures to
Volatile Toxicants (4)
The mixture TLV-TWA can be computed by
n
(TLV  TWA ) mix 
C
i 1
i
n
Ci

i 1 (TLV  TWA ) i
If the sum of the concentration of the
toxicants in the mixture exceeds this
amount, then the workers are over-exposed.
Evaluating Exposures to Dusts
• Toxicological theory teaches that dust
particles which present the greatest hazard
to the lungs are normally in the particle size
range of 0.2 to 0.5 microns.
• Dust evaluation calculations are done in an
identical manner to volatile vapor.
Noise
• Noise levels are measured in decibels. A
decibel is a relative logarithmic scale used
to compare the intensity of two sounds.
 I0 
Noise Intensity(dB)  10 log10  
I 
 
• For convenience, the hearing threshold is
set at 0 dBA. (Table 2-5, Table 2-6)
Evaluating Exposures to Noise
Noise evaluation calculations are performed
identically to calculations for vapors except
that dBA is used instead of ppm and
exposure hours is used instead of TLV-TWA.