Sampling Guide for Air Contaminants in the Workplace - Irsst

14 IRSST – Sampling Guide for Air Contaminants in the Workplace
Equation 11: Calculating the R m (sum of the fractions of the mixture)
C = Weighted concentration of each of the substances in the air (MDE)
T = TWAEV
1,2,...n = Indication of each of the substances
C1
C2
C
R
m
= + + ... +
T T T
1
2
n
n
When R m exceeds unity, the permissible concentration of the mixture is exceeded and the exposure does not
comply. In the case of an unusual schedule, the TWAEV (T, 8 hours) must be replaced by the AMEV (T a ,
work period).
• Example 1
An operator works for 7 hours and 20 minutes at a task in which he is exposed to a substance listed in
Schedule I of the ROHS. The concentration measured during this period is 0.12 mg/m 3 . What is his mean
daily exposure (MDE)?
7.33 hours at 0.12 mg/m 3
0.67 hours at 0 mg/m 3 (no exposure) namely: MDE = ((0.12 x 7.33) + (0 x 0.67)) / 8 = 0.11 mg/m 3
• Example 2
An operator works for 8 hours on a process in which he is exposed to a contaminant for which the ROHS
gives a TWAEV. During this period, he is exposed to a concentration of 0.15 mg/m 3 . What is his mean daily
exposure?
MDE = (0.15 x 8) / 8 = 0.15 mg/m 3
• Example 3
An operator works for 8 hours during the night on a process that exposes him intermittently to a regulated
substance. Knowing his work schedule and his exposure during these different tasks (Table 2), what is his
mean daily exposure?
Table 2- Evaluation of the exposure of worker Y
Work
schedule
Task
Exposure values
(mg/m 3 )
Sampling time in
hours
22:00 - 24:00 Shop assistant
0.1 (from exposure values of a group of full-time
workers performing this task)
2
24:00 - 01:00 Office work 0 1
01:00 - 04:00 Cafeteria work 0 3
04:00 - 06:00 Cleaning in shop 0.21 (measured) 2
The exposure was established to be zero for the office and cafeteria work, and consequently his mean daily
exposure will be:
MDE = ((0.10 x 2) + (0.21 x 2) + (0 x 4)) / 8 = 0.078 mg/m 3
• Example 4
Workers are exposed to solvents under the conditions described in Table 3. Are the workers overexposed to
these solvents, which all have effects on the central nervous system?