Information card 7
Limit Values
The following chart shows limits of common hazardous gases in shipping containers. For
part of these gases there is a legal limit. Substances for which no legal limit exists, the limit
(formerly MAC value) used is the one that was in force until January 1, 2007 in the
Netherlands. It gives the following summary:
Name of substance
Ammonia*
Benzene*
Hydrocyanic acid*
Chloropicrin**
1,2-Dichloroethane*
Formaldehyde*
Phosphine*
Carbon dioxide*
Carbon monoxide*
Methyl bromide**
Sulfuryl fluoride**
CASnumber
7664-41-7
71-43-2
74-90-8
76-06-2
107-06-2
50-00-0
7803-51-2
124-38-9
630-08-0
74-83-9
2699-79-8
Styrene**
100-42-5
Toluene*
108-88-3
Xylene*
1330-20-7
Oxygen***
Explosive limit
Information card 7 Limit Values
© Healthy Transport, February
2011
TGG 8
hour
mg/m3
14 (ppm)
(20)
3,25
(1)
1
(0,9)
0,7
(0,1)
7
(1,5)
0,15
(0,1)
0,14
(0,1)
9000
(5000)
29
(25)
1
(0,3)
10
(2,5)
86
(20)
150
(40)
210
(48)
TGG 15 min
mg/m3
H
36
H
10
H
0,5
0,28
H
172
384
442
H
19 – 21%
Maximum 10%
Page 1 of 5
Explanation of the chart:
*
**
***
Legal limit under the Working Conditions Decree (Articles 4.3 and 4.16)
Applicable MAC limit until January 1, 2007. Sometimes called the
indicative limit.
Regarding the oxygen content, the Working Conditions Decree uses a
concentration below 18 volume percent as a minimum. However below 19 volume
percent working becomes quite difficult because the oxygen exchange in the
blood is hampered. Healthy Transport (Gezond Transport) recommends a minimum
of 19 volume percent.
CAS-number
To facilitate unequivocal identification every substance has had a so-called CASnumber added, i.e. the number under which the ‘Chemical Abstract’ Service registers
the substance.
TWA
Time Weighted Average. In addition to the maximum allowable concentration for an
exposure time of 8 hours a day, for some substances a limit is also set for short-term
exposure of up to 15 minutes.
H: Skin absorption
Substances that are absorbed relatively easily by the skin, which could mean a substantial
contribution to the total internal exposure, are designated with an H.
In addition to measures against inhalation of these substances, appropriate measures need to be
taken to avoid skin contact.
Information card 7 Limit Values
© Healthy Transport, February
2011
Page 2 of 5
Information about limits
Public and private limits
In January 2007, a revised limit system was introduced. The old system of
Maximum Allowable Concentrations (MAC-values) has been replaced by legal limits. These are
set by the government and published on www.ser.nl.
Industry needs to draw up private limits for other substances; working with these substances
should not lead to immediate or long-term health problems for the employee or his offspring.
What is a limit value?
A limit value is the permissible limit of concentration of a substance in the breathing zone of a
worker. The limit indicates that during a forty-year exposure there is no risk of health hazards.
The limit can be indicated in a Time Weighted Average (TWA) or a Ceiling value (C.)
The Time Weighted Average (TWA) is usually based on an average over an eight-hour
working day (TWA 8 hours). During the working day the limit –TWA 8 hours- may not be
exceeded. For some substances with immediate toxic effects time weighted averages of 15
minutes have been set (TWA 15 minutes). TWA 15 minutes is the limit for short-term peak
exposure, when during the rest of the day no or negligible exposure to hazardous
substances occurs. If a TWA 15 minutes has not been set for a substance the labor
inspectorate uses the limit of the TWA 8 hour multiplied by a factor 2 as a guideline. This
does not apply for carcinogenic, mutagenic or reprotoxic Substances.
A limit such as a ceiling value (C) indicates that this limit should not be exceeded at
any time.
De limits have been established to cover situations where hazardous substances are inhaled.
They do not offer protection from exposure in other ways such as through the skin and by
ingestion. When a substance (such as benzene) is known to be easily absorbed by the skin, the
limit value gets a notation H for Skin exposure.
On the website of SER (Social and Economic Council of the Netherlands, www.ser.nl) it is
possible to look up the CAS number through the substance name and what is the current
limit. On this website the indicative limits are also mentioned. These are the former MAC
limits and limits that apply in other European countries.
Carcinogenic, mutagenic and reprotoxic substances
Carcinogenic substances can cause cancer, mutagenic substances can change the
genetic material of man and reprotoxic substances can have a negative effect on
fertility and the unborn child.
Carcinogenic, reprotoxic and mutagenic substances are subject to a different approach.
These substances lack a safe threshold. The lowest possible exposure (none) should
always be aimed for. And here the possibility to go twice the limit during a brief exposure
does not apply.
Information card 7 Limit Values
© Healthy Transport, February
2011
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Insufficient protection
Limits are generally geared to providing safety to a healthy population of male
employees. A limit may not offer full protection if employees carry out heavy
physical labor. In determining limits, figures are based on an average ‘respiratory
minute volume’ of employees. However, when performing heavy physical labor more
air than on average is inhaled which could cause an excessive amount of substance
to be absorbed. The same effect is caused when working hours exceed 8 hours per
day. In addition limits offer insufficient protection to special groups of employees
who have a reduced capability, such as pregnant women and young people.
Combined exposure (addition rule)
Limits have been established for single substances. When exposed to a combination of
substances of which it is known that the individual components have the same toxic effect on
an organ system, the so-called addition rule applies when testing the limits. With the
addition rule the sum of all the individual exposure situations, as a fraction of the
individual limits, has to be less than 1. In other words:
(C1 / limit1) + (C2 / limit2) + (C3 / limit3) + (Cn / limits) < 1
Where:
Cn is the exposure concentration to substance n
limitn is the limit for substance n
This is for instance the case with exposure to various organic solvents, such as the
combination of exposure to toluene, xylene, alkene, methyl ethyl ketone, gasoline, kerosene,
alcohols, ketones, aldehydes, etc. The evaporation problem in shipping containers is rarely a
question of one single hazardous substance.
Deployment of specialists
When exposure for employees varies during a working day in terms of diversity of
substances or in terms of duration of the exposure or when a brief exposure of 15
minutes occurs more than once per working day, it is recommended to have the risk
assessed by a specialist (for example an occupational health specialist).
Information card 7 Limit Values
© Healthy Transport, February
2011
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Examples of calculations
- Brief exposure
On a working day an employee opens one shipping container, which is known to
contain methyl bromide. The exposure time is << 15 minutes. During the rest of the
day no more exposure to hazardous substances takes place. A TWA has not been
established. The limit that is tested is double the TWA- 8 hours.
It should be noted that in the limit an H is shown. This means that skin absorption
can contribute substantially to internal exposure. Proper skin protection is
(necessary) even during brief exposure.
-
Brief exposure to a carcinogenic substance
On a working day an employee opens one shipping container, which is known to
contain benzene. Exposure is < 15 minutes. During the rest of the day no more
exposure to hazardous substances takes place.
Because benzene is a carcinogenic substance it remains, in spite of the brief
exposure, at a maximum of 3,25 mg/m3 (TWA-8 hours). Nevertheless the employer
has the duty to keep exposure to benzene to a minimum (avoid it altogether).
-
Combined exposure (addition rule)
An employee offloads two similar shipping containers using a forklift. He does this
throughout his working day. It is known that the shipping containers contain various
solvents (including toluene and xylene). In a situation such as this the addition rule
applies.
-
Combined exposure in combination with heavy physical labor
An employee manually offloads two similar shipping containers. He does this
throughout his working day. It is known that the shipping containers contain various
solvents (including toluene and xylene). In a situation such as this the addition rule
applies. In addition, the manual offloading of a container is physically demanding
work. It must therefore be taken into account that the current limits do not offer
adequate protection. What percentage of the limit does offer adequate protection has
not been established.
Information card 7 Limit Values
© Healthy Transport, February
2011
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