Chlorine dioxide

Flammability

Link to relevant study record(s)

Reference

Reference 1

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

Reference 2

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.

Reference 3

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.

Reference 4

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%.

Reference 5

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.

Reference 6

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.

Reference 7

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.

Reference 8

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 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 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, t_init, and time for pressure increase t_Pmax, 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.

Reference 9

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.

Reference 10

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.

Reference 11

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.