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Please be aware that this old REACH registration data factsheet is no longer maintained; it remains frozen as of 19th May 2023.

The new ECHA CHEM database has been released by ECHA, and it now contains all REACH registration data. There are more details on the transition of ECHA's published data to ECHA CHEM here.

Diss Factsheets

Physical & Chemical properties

Flammability

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Endpoint:
flammable solids
Data waiving:
study technically not feasible
Justification for data waiving:
the study does not need to be conducted because the substance is a liquid
Endpoint:
flammable gases
Type of information:
not specified
Adequacy of study:
other information
Reliability:
4 (not assignable)
Rationale for reliability incl. deficiencies:
secondary literature
Remarks:
Data comes from reviews using secondary data sources, and therefore cannot be assigned as reliable.
Reason / purpose for cross-reference:
reference to same study
Reason / purpose for cross-reference:
reference to other study
Principles of method if other than guideline:
No data.
Parameter:
lower explosion limit
Value:
> 10 % (not further specified)
Remarks on result:
other: %v/v at atmospheric pressure

Chlorine dioxide gas is explosive in concentrations in excess of 10% v/v at atmospheric pressure and will easily be detonated by sunlight or heat.

Executive summary:

The international CICAD review and the OECD SIDS report provide a lower explosion limit (LEL) of 10%v/v for the gas Chlorine dioxide, from the Merck Index.

Endpoint:
flammable gases
Type of information:
not specified
Adequacy of study:
other information
Reliability:
4 (not assignable)
Rationale for reliability incl. deficiencies:
secondary literature
Remarks:
Data comes from a sheet with no reference to data sources, and therefore cannot be assigned as reliable.
Reason / purpose for cross-reference:
reference to same study
Principles of method if other than guideline:
No data.
Parameter:
lower explosion limit
Value:
> 10 % (not further specified)
Remarks on result:
other: vol% in air
Executive summary:

The ICSC provides information on explosive limits, with a LEL >10%vol in air for the substance Chlorine dioxide.

Endpoint:
flammability
Type of information:
not specified
Adequacy of study:
other information
Reliability:
4 (not assignable)
Rationale for reliability incl. deficiencies:
secondary literature
Remarks:
Data comes from an online compilation using secondary data sources, and therefore cannot be assigned as reliable. However, please note that the endpoint is cited in the database as peer reviewed.
Reason / purpose for cross-reference:
reference to same study
Reason / purpose for cross-reference:
reference to other study
Principles of method if other than guideline:
No data.

Concentrations above 10% can ignite at 130 deg C. Oxidizable organic dusts can lower decomposition temperature.

Executive summary:

The HSDB database provides information on the fire potential of Chlorine dioxide: the substance can ignite from 130°C if concentration is higher than 10%.

Endpoint:
flammable gases
Adequacy of study:
other information
Reliability:
4 (not assignable)
Rationale for reliability incl. deficiencies:
secondary literature
Remarks:
The publication summarises observations from other references, but doesn't provide experimental details; therefore it cannot be assigned as reliable.
Reason / purpose for cross-reference:
reference to same study
Reason / purpose for cross-reference:
reference to other study
Parameter:
lower explosion limit
Value:
35 % (not further specified)
Remarks on result:
other: 310 mm Hg

In Torregrossa's paper (9), experiments were done with ClO2/air mixtures: detonation was never observed, even up to 35% v/v in air (310 mm Hg), even though Haller & Northgraves (1) did observe it at partial pressures above 300 mm Hg.

The unknown and presumed dangerous area is with pure ClO2 at pressures above about 130 mm Hg, and diluted in air at atmospheric pressure or higher with partial pressure above 300 mm Hg.

In practice, values above 100 mm Hg are carefully avoided.

Executive summary:

As an introduction to safety management in chlorine dioxide plants, this publication summarises observations from other references about explosive concentration of the substance, whether pure or diluted in air, and practical maximum recommended limit.

Endpoint:
flammable gases
Type of information:
not specified
Adequacy of study:
other information
Reliability:
4 (not assignable)
Rationale for reliability incl. deficiencies:
secondary literature
Remarks:
Data comes from a book dedicated to chlorine dioxide, compiling very numerous literature references, but few experimental details are provided. Therefore it cannot be assigned as reliable
Reason / purpose for cross-reference:
reference to same study
Reason / purpose for cross-reference:
reference to other study
Principles of method if other than guideline:
No data.
Parameter:
lower explosion limit
Value:
4 - 10 % (not further specified)

Gaseous ClO2

Depending upon its concentration in the vapour phase, chlorine dioxide can undergo a spontaneous autodecomposition reaction depending on partial pressure and temperature. At concentrations above about 4% in the air, a spark can cause a decomposition reaction with evolution of a small amount of energy [Rosenblatt 1976]. At ambient temperature, e.g. < 30°C, and concentrations above about 10%, the gas may undergo a spontaneous decomposition reaction (with a long induction period) commonly referred to as a "puff" [Gall 1976; Gray and Ip 1972; Haller and Northgraves 1955; Ip and gray 1972; McHale and von Elbe 1968; Noack and Doerr 1979; Paillard et al. 1986; Schumacher and Stieger 1930], because its flame propagation if ca 1 m/s, when compared to the flame propagation wave of an explosion, i.e., ca 300 m/s, is relatively quite slow.

As the concentration of chlorine dioxide in the vapour state increases, the violence of this reaction increases. At a concentration about 17% in the vapour state, the explosion becomes quite energetic, to the point where rapid, unscheduled disassembly of equipment can occur. However, a concentration of about 20% chlorine dioxide has been produced in the vapour space routinely with no problem [Haller and Northgraves 1955].

Gaseous ClO2 can decompose with a "puff" at partial pressures at or above 80 mm Hg.

Aqueous solutions of ClO2

Henry's law states that a gas dissolved in solution will distribute itself into the vapour phase in proportion to its concentration in solution. Therefore, the safe solubility of ClO2 depends upon temperature and pressure, and thus, by controlling the concentration of chlorine dioxide in solution, the partial pressure of chlorine dioxide can be controlled. That is, if the aqueous concentration of chlorine dioxide is kept below certain well established limits, chlorine dioxide cannot achieve that concentration in the vapour phase which can "puff". At 25°C and 30 mm partial pressure, it is safely soluble to the extent of about 3 g/L. What this means is that a solution of about 3 g/L concentration can be placed in a sealed container with an air space, and ClO2 will achieve a concentration in the air space according to Henry's law (54 atm at 20°C) that will not, at 25°C, undergo a "puff" (explosive decomposition). Relatively high concentrations of ClO2 can be stored safely for long periods, as long as there is no air space for the ClO2 gas to form.

Below about 30°C, if the partial pressure of chlorine dioxide is kept below about 50 mm Hg, and if organics or other impurities are not present, an explosive concentration of chlorine dioxide in the vapour space cannot be achieved [Ingols and Ridenour 1948a; McHale and von Elbe 1968].

Above about 45°C (the lower temperature limit), ClO2 vapour appears to always decompose, regardless of its partial pressure.

Executive summary:

The Simpson's book, dedicated to chlorine dioxide, provides summaries of several studies on explosivity of the substance. For the gas, a lower explosion limit of 10%v/v is suggested, but can be lowered to 4% in case of ignition by sparks. For off-gassing of aqueous solution, a conservative safe upper limit for partial pressure of about 50 mm Hg (6666 Pa) is generally accepted, which can be controlled from concentration and temperature. Above 45°C, ClO2 vapor appears to always decompose.

Endpoint:
flammable gases
Type of information:
not specified
Adequacy of study:
other information
Reliability:
4 (not assignable)
Rationale for reliability incl. deficiencies:
secondary literature
Remarks:
Data comes from a toxicological profile citing other data sources, and therefore cannot be assigned as reliable. However, please note that secondary source is considered as peer reviewed.
Reason / purpose for cross-reference:
reference to same study
Reason / purpose for cross-reference:
reference to other study
Principles of method if other than guideline:
No data.
Parameter:
lower explosion limit
Value:
> 10 % (not further specified)
Remarks on result:
other: %v/v at 1 atm

Explosive at temperatures >-40 °C [1] and concentrations in excess of 10% v/v at 1 atm [2].

Executive summary:

The peer reviewed ATSDR profile for the substance Chlorine dioxide provides information relating to its explosive limits.

Endpoint:
flammable gases
Type of information:
experimental study
Adequacy of study:
other information
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
study well documented, meets generally accepted scientific principles, acceptable for assessment
Remarks:
This experimental study does not follow internationally recognised guidelines, and therefore cannot be fully reliable. It is nevertheless well documented, and acceptable under the test conditions.
Reason / purpose for cross-reference:
reference to same study
Principles of method if other than guideline:
A thermoregulated vessel, with pressure recording, is filled with chloride dioxide produced in-situ. Ignition is achieved with an AC electric arc.
GLP compliance:
no
Parameter:
lower explosion limit
Value:
5.6 % (not further specified)
Remarks on result:
other: partial pressure of 10 mbar at a total of 170-180 mbar (molar fraction equivalent to %vol)
Parameter:
upper explosion limit
Remarks on result:
not measured/tested

The experiments and their results are summarized in the following tables, showing the dependence of tinit, and tPmax and f on the partial pressure of ClO2 and water.

Date

GA

Temp (°C)

Cooling

Water inj (µL)

Pressure (mbar) registered

Pressure (mbar) corrected

Ignition

Explosion times (ms)

Explosion pressures (mbar)

f

In

Surf

°C

PH2O (mbar)

ClO2

Air

H2O

Total

ClO2

Air

H2O

Total

(sec)

(J)

tinit

tPmax

Pmax

Pfinal

A

20.9

102

72.8

76.0

11

13

150

102

5

90

197

89

5

103

197

0.35

14

10

15

760

236

3.9

C

 

 

 

 

 

 

150

110

5

91

206

97

5

104

206

 

 

7

14

520

259

2.5

1

27.9

 

67.0

75.6

11

13

250

50

7

197

254

37

7

210

254

0.35

14

15

45

550

264

2.2

2

 

112

 

75.8

 

 

200

49

8

142

199

36

8

155

199

 

 

12

30

500

200

2.5

3

 

 

68.4

75.8

 

 

200

44

7

160

211

31

7

173

211

 

 

15

42

470

225

2.2

4

 

 

70.0

75.6

11

13

200

40

4

166

210

27

4

179

210

 

 

15

49

450

220

2.1

5

 

 

70.2

75.9

 

 

200

36

25

120

181

23

25

133

181

 

 

15

45

400

194

2.2

6

 

101

70.2

75.9

11

13

200

36

8

162

206

23

8

175

206

 

 

15

62

410

216

2.0

7

 

 

71.1

76.0

 

 

300

36

7

191

234

23

7

204

234

 

 

30

85

410

-

1.8

8

 

 

71.1

76.0

 

 

300

36

5

215

256

23

5

228

256

 

 

35

92

430

263

1.7

9

 

 

 

76.8

11

13

200

97

6

120

223

84

6

133

223

 

 

40

-

850

263

3.8

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

12

28.11

101

12

10

6

9

-

24

 

 

24

15

 

9

24

0.35

14

8

18

84

-

3.5

13

 

 

18

18

 

 

-

21

 

 

21

12

 

9

21

 

 

-

-

ca80

31

ca4

14

 

 

18

18

 

 

-

23

 

 

23

14

 

9

23

 

 

10

12

117

32

5.1

15

29.11

102

33

42

6

9

-

20

 

 

20

11

 

9

20

 

 

8

8

108

29

5.4

16

 

 

41

45

 

 

-

19

 

 

19

10

 

9

19

 

 

12

15

83

24

4.4

17

 

 

41

45

 

 

-

20

 

 

20

11

 

9

20

 

 

7

10

104

29

5.2

18

3.4

 

67.3

72.0

4

8

200

15

7

161

183

7

7

169

183

0.35

14

60

170

268

187

1.46

19

 

 

 

 

 

 

200

26

26

159

211

18

26

167

211

 

 

-

-

370

217

1.75

20

 

 

 

 

 

 

200

25

11

139

175

17

11

147

175

 

 

16

-

370

190

2.11

21

18.4

 

67.0

71.5

4

8

200

19

18

143

170

11

18

151

170

0.35

14

40

125

275

ca180

1.62

22

 

 

 

 

 

 

200

21

21

150

192

13

21

158

192

 

 

-

-

301

201

1.50

23

 

 

 

 

 

 

200

21

13

141

175

13

13

149

175

 

 

25

100

300

188

1.60

Decomposition of the ClO2could not be avoided. Even with extremely low partial pressures (10 mbar and less), pressure increases of 50% (f ca 1.5) were registered. The pressure factor f rises with increasing partial pressure of ClO2. Time of initiation, tinit, and time for pressure increase tPmax, are strongly dependent on the ClO2partial pressure. It can also be stated that water is a very good inhibitor for the decomposition, a fact which is also mentioned in the literature. It should be pointed out that experiments N°12-17 with only 9 mbar, all of which emerging from NaClO2water solution, also were performed at lower temperatures and lower total pressures than the others.

As decomposition are taking place at partial pressures of ClO2 which are thought to be completely safe (based on literature), the equipment was controlled, the pressure transducers have been calibrated, no decomposition is registered on the oscilloscope with pure air in the explosion vessel. The conclusion has been that the ignition energy is too high. It is also well-known that an electric arc is producing a rather high amount of UV-light, which in the literature (McHale 1968, Crawford 1968) has been mentioned as a very potent decomposition source. According to the characteristics of the AC arc (see above), it is difficult to both calculate and regulate (decrease) the energy effectively. With an ignition time of 0.35 second, the nergy can be calculated to 2000 V x 20 mA x 0.35 sec = 14 J.

Conclusions:
In particular conditions, chlorine dioxide can explode at partial pressure as low as 1000 Pa (eq. to a concentration of 5.6%vol).
Executive summary:

Explosion trials with ClO2, conducted according to a non-standardised method, indicate that this gas is very sensitive to an (AC) electric arc as ignition source. Decomposition was recorded with only 10 mbar of ClO2 at a total of 170-180 mbar, the rest being mostly water vapour. This is far below what is normally said to be the lower explosion limit (ca 80 mbar). This was supposed to be due to the high energy and/or UV release of the ignition source.

The initiation period before explosion and the time to reach maximum pressure are longer, the lower the ClO2 pressure is. The pressure rise factor (Pmax/Pstart) decreases linearly with the ClO2 pressure. Water was confirmed to be a good inhibitor.

Endpoint:
flammable gases
Type of information:
not specified
Adequacy of study:
other information
Reliability:
4 (not assignable)
Rationale for reliability incl. deficiencies:
secondary literature
Remarks:
The reference cites only endpoint information as a secondary source, and therefore cannot be assigned as reliable.
Reason / purpose for cross-reference:
reference to same study
Reason / purpose for cross-reference:
reference to other study
Parameter:
lower explosion limit
Value:
11 % (not further specified)

Concentration of ClO2 vapour at about 11% in air may give mild explosions or "puffs", and concentrations of over 4% in air may be set off by an electric spark to sustain a decomposition wave.

Executive summary:

This publication cites, as a secondary source, data on the explosive portential for the gas chlorine dioxide: a general limit of 11% is set, which can be lowered to 4% in case of ignition by electric sparks.

Endpoint:
flammable gases
Type of information:
not specified
Adequacy of study:
other information
Reliability:
4 (not assignable)
Rationale for reliability incl. deficiencies:
data from handbook or collection of data
Remarks:
Data comes from a handbook using secondary data sources, and therefore cannot be assigned as reliable. However, please note that it is a compilation of numerous information, and considered as a reference among literature on hazardous reactions.
Reason / purpose for cross-reference:
reference to same study
Reason / purpose for cross-reference:
reference to other study
Principles of method if other than guideline:
No data.
Parameter:
lower explosion limit
Value:
> 7 % (not further specified)

(...) it was stated that decomposition by sparking begins to become hazardous at concentrations of 7–8% in air [3], and that at 10% concentration in air (0.1 bar partial pressure) explosion may occur from any source of initiation energy, such as sunlight, heat or electrostatic discharge [5].

Executive summary:

The Bretherick's handbook compiles information on explosive potential of Chlorine dioxide, including data on LEL = 10% in air for any source of initiation, and even 7-8% if sparks.

Endpoint:
substances / mixtures which in contact with water emit flammable gases
Data waiving:
study scientifically not necessary / other information available
Justification for data waiving:
the study does not need to be conducted because the experience in production or handling shows that the substance does not react with water, e.g. the substance is manufactured with water or washed with water
Justification for type of information:
Flammability if contact with water is of no concern, based on the weight of evidence that the substance is generated as aqueous solution.

Description of key information

Chlorine dioxide gas: LEL = 4 (sparks) - 10 (any source of ignition) %v/v in air.

Key value for chemical safety assessment

Flammability:
not classified

Additional information

An experimental, non-standard, study is available, as well as numerous literature data regarding explosive properties of chlorine dioxide gas and safe management. A Lower Explosion Limit of 10 %v/v in air is generally recognised, except in case of ignition by sparks, where lower values, between 4 and 8%, are set. For safety reasons, the lowest concentration will be retained in the present dossier.


Flammability if contact with water is of no concern, based on the weight of evidence that the substance is generated as aqueous solution.

Justification for classification or non-classification

Solution of chlorine dioxine generated in-situ at less than 2% in water (as registered): This endpoint does not apply to the substance as registered (aqueous solution generated in-situ), as liquid.


Other information: The gas has a Harmonised Classification as Oxidising, therefore it does not need to be classified in any other hazard class.