Chlorine dioxide

Explosiveness

Link to relevant study record(s)

Reference

Reference 1

Endpoint:

explosive properties of explosives

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:

other: Explosive under influence of flame

Remarks:

migrated information

Remarks on result:

positive (not further specified)

Parameter:

other: Explosive (not specified)

Remarks:

migrated information

Remarks on result:

positive (not further specified)

Remarks:

sunlight

May explode on heating, on exposure to sunlight or if subjected to shock or sparks.

Executive summary:

The ICSC provides information relating to explosive potential of the Chlorine dioxide, when heated, exposed to sunlight, or subjected to shock or sparks.

Reference 2

Endpoint:

explosive properties of explosives

Type of information:

not specified

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:

other: Explosive (not specified)

Remarks:

migrated information

Remarks on result:

positive (not further specified)

Liquid ClO₂ is extremely unstable and dangerously explosive. The slightest shock will initiate detonation and decomposition to chlorine and oxygen.

Gaseous ClO₂ exhibits a very peculiar property, in that it "auto-decomposes", following an induction period. These properties have been studied extensively by many workers (ref.1,2,3,4,7,8). The induction period is related to the surface/volume ratio of the equipment, and the partial pressure of ClO₂ and temperature. The force of the ensuing explosion is determined by ClO₂ concentration, the presence of oxidisables, the location of the explosion, and the shape and size of the equipment containing it. (...) As the decomposition products are oxygen and chlorine, the ClO₂ decomposition can initiate a second more powerful explosion if reducing agents such as methanol are present, or with standing flames, the decomposition can initiate thermite fires in metal equipment. In addition to these peculiarities, the mechanism of decomposition of chlorine dioxide is via a branched chain mechanism, so that not only is there no prior warning of an explosion, but the resulting burning velocity and detonation forces can be extremely high. It is postulated that ClO₂ is the key intermediate in the burning of ammonium perchlorate (ref.5,6), and thus contributes to its high velocity and efficiency as a solid rocket fuel.

Interpretation of results:

explosive

Remarks:

Migrated information

Executive summary:

As an introduction to safety management in chlorine dioxide plants, this publication summarises observations from other references about explosive properties of the substance, in particular parameters that can influence the induction period, and the gravity of the consequences.

Reference 3

Endpoint:

explosive properties of explosives

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 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:

other: Explosive (not specified)

Remarks:

migrated information

Remarks on result:

positive (not further specified)

Chlorine dioxide is considerably endothermic (deltaH°_f (g) +103.3 kJ/mol, 1.53 kJ/g) and of limited stability. It is a powerful oxidant and explodes violently on the slightest provocation as gas or liquid [1]. It is initiated by contact with several materials, on heating rapidly to 100°C or on sparking [2], or by impact as solid at -100°C [3]. A small sample exploded during vacuum distillation at below -50°C [4], and 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]. A kinetic study of the decomposition shows that it is explosive above 45°C even in absence of light, and subject to long induction periods due to formation of intermediate dichlorine trioxide. UV irradiation greatly sensitises the dioxide to explosion [6]. The solid (a dimer) can be relatively safely handled below -40°C and the gas at pressures below 50 mbar [7]. A guide on fire and explosion hazards in industrial use of chlorine dioxide is available [8], and preparative precautions have been detailed [9]. An improved and safer method for continuous production of chlorine dioxide is claimed [10]. A thorough review has been written, detailing numerous incidents, of hazards attending industrial preparation and use of chlorine dioxide (now much used as a low chlorine bleach). Liquid ClO₂ can separate from aqueous solutions >60 g/l, it is exceedingly shock sensitive. A partial pressure of 130 mbar in air is thought entirely safe, as are aqueous solutions (but not necessarily the head space above them) [11]. The safe use of chlorine dioxide and sodium chlorite has been reviewed [12].

Interpretation of results:

explosive

Remarks:

Migrated information

Executive summary:

The Bretherick's handbook compiles information on explosive potential of Chlorine dioxide, from twelve secondary references, showing evidence of high sensitivity.

Reference 4

Endpoint:

explosive properties of explosives

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:

other: Explosive under influence of flame

Remarks:

migrated information

Remarks on result:

positive (not further specified)

Parameter:

other: Explosive (not specified)

Remarks:

migrated information

Remarks on result:

positive (not further specified)

Remarks:

sunlight

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 (Budavari et al., 1996).

It is marketed and transported as a stabilized aqueous solution generally less than 1% w/v (more concentrated forms are explosive).

Executive summary:

The international CICAD review and the OECD SIDS report provide information relating to explosive potential of the gas Chlorine dioxide, cited from the Merck Index, when heated or exposed to sunlight. Dilute aqueous solutions are stable (<1%w/v).

Reference 5

Endpoint:

explosive properties of explosives

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.

Parameter:

other: Explosive (not specified)

Remarks:

migrated information

Remarks on result:

positive (not further specified)

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

N°	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 ClO₂ could 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, t_init, and time for pressure increase t_Pmax, are strongly dependent on the ClO₂ partial 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 NaClO₂ water 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.

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.

Reference 6

Endpoint:

explosive properties of explosives

Type of information:

not specified

Adequacy of study:

supporting study

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:

other: Explosive (not specified)

Remarks on result:

positive (not further specified)

Aqueous ClO₂

Aqueous ClO₂ has no explosive properties.

Gaseous ClO₂

The most commonly promoted characteristic of chlorine dioxide is that it is an explosive gas.

Much work has been done to investigate its explosive properties [Schumacher and Stieger 1930; Haller and Northgraves 1955; McHale and von Elbe 1967; Crawford and Dewitt 1968; McHale and von Elbe 1968; Gray and Ip 1972; Ip and gray 1972; Torregrossa et al. 1976; Paillard et al. 1986; Lopez et al. 1994]

When ClO₂ is placed in a closed vessel, under some circumstances the gas can decompose energetically. The energy of the decomposition reaction increases with concentration of chlorine dioxide in the gaseous phase. Depending on a number of factors, there is an induction period where no temperature increase is noted, prior to explosive decomposition. Several factors influence the induction period. These include the surface/volume ratio of the container, the partial pressure of ClO₂, and the temperature. The force of the ensuing decomposition is determined by the ClO₂ concentration, the presence of oxidizable material, and the shape and size of the equipment containing the gaseous ClO₂. The velocity of the decomposition wave is about 1 m/sec at 130 mm Hg pressure and about 3°C; at 207 mm Hg, the velocity of the wave is about 2 m/sec [Haller and Northgraves 1955]. As partial pressure increases, the violence of the reaction increases so that a detonation occurs at 300 mm Hg.

Uncontaminated gaseous ClO2 only explodes above a temperature of 88°C; below that temperature, only an exotherm is observed [Gilmont 1968]. Water has a strong inhibiting effect on the decomposition of gaseous ClO2 up to 90°C [Crawford and Dewitt 1968].

Due to its sensitivity to temperature, pressure and shock, it is impossible to store or ship as a pure liquid or a compressed gas.

Liquid ClO₂

Above melting temperature (-59°C), ClO₂ forms a red, unstable liquid which is very explosive at temperatures above -40°C. Liquid ClO2 will also separate from aqueous concentrated solutions (for example above 60 g/L at normal temperatures). Pure liquid ClO₂ is sensitive to shock and light, and decomposes with about 1/3 of the force of TNT [Sattelberger et al. 2002].

Executive summary:

The Simpson's book, dedicated to chlorine dioxide, summarizes several studies on its explosive properties.

Gaseous ClO₂ can decompose explosively as a function of temperature and pressure. The decomposition can be triggered by a spark. The induction time can be substantially decreased by the presence of impurities, which include gaseous organics, or oxidizable materials, which include rubber, cork, or sulfur. At a constant temperature, as the partial pressure of ClO₂ increases, the violence of the reaction increases.

Aqueous ClO₂ has no explosive properties.

Reference 7

Endpoint:

explosive properties of explosives

Data waiving:

study scientifically not necessary / other information available

Justification for data waiving:

other:

Justification for type of information:

In accordance with column 2 of REACh Annex VII, the study does not need to be conducted if, for mixtures of inorganic oxidising substances (UN Division 5.1) with organic materials, the concentration of the inorganic oxidising substance is less than 15% by mass, if assigned to UN Packaging Group I (high hasard) or II (medium hasard).
Note also that Simpson (2005) reports that aqueous ClO2 has no explosive properties.
Finally, no physical hazard is established in the harmonised entry and according the above observations. However, based on the potential hazard if off-gassing, the EUH018 phrase is proposed.

Reference 8

Endpoint:

explosiveness

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.

Parameter:

other: Explosive under influence of flame

Remarks:

migrated information

Remarks on result:

positive (not further specified)

Parameter:

other: Explosive (not specified)

Remarks:

migrated information

Remarks on result:

positive (not further specified)

Remarks:

sunlight

Explodes when heated or by reaction with organics. [1]

In concentrations in excess of 10%, 1 atm, easily detonated by sunlight, heat, contact with mercury or carbon monoxide. [2]

Explosive decomposition at 100 deg C. Explosive hazard by heating, exposing to sunlight, contacting mercury or carbon monoxide. [3]

Executive summary:

The HSDB database provides information, from several sources, relating to explosive potential of the substance Chlorine dioxide, when heated or exposed to sunlight.

Description of key information

Solution of chlorine dioxine generated in-situ at less than 2% in water (as registered): not considered to be explosive, but potential hazard if off-gassing.

Key value for chemical safety assessment

Explosiveness:

non explosive

Additional information

The properties of gaseous chlorine dioxide are discussed because, although the substance as registered is in-situ generated aqueous solution, under certain conditions off-gassing may occur. Thus, the properties of gaseous chlorine dioxide, as well as the properties of the aqueous solution are important.

An experimental, non-standard, study is available, as well as numerous literature data regarding explosive properties of chlorine dioxide gas and safe management. The gas is well-known to be sensitive to various sources of ignition (heat, light, shock, and in particular sparks), and is characterised by an induction period.

Water was shown to be a good inhibitor, and diluted aqueous solutions are considered to be stable. Partial pressure of ClO₂ over the solution, and therefore potential hazard, is a function of concentration and temperature (please refer to points 4.6 and 4.13).

Justification for classification or non-classification

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

For chlorine dioxide in aqueous solution, no physical hazard is established in the harmonised entry. However, based on the potential hazard if off-gassing, the EUH018 phrase will be proposed.