Potential Explosion Hazard of Carbonaceous Nanoparticles:

Explosion Parameters of Selected Materials

Supplemental Material

Submitted to

Journal of Hazardous Materials

Leonid A. Turkevich*

Centers for Disease Control and PreventionNational Institute for Occupational Safety and Health,

Division of Applied Research and Technology,1090 Tusculum Avenue, MS-R7, Cincinnati, OH 45226 USA

and

Ashok G. Dastidar, Zachary Hachmeister, Michael Lim

Fauske & Associates, LLC16W070 83rd Street

Burr Ridge, IL 60527 USA

* corresponding author:

LLT0@cdc.govPhone: (513) 841 4518

Fax: (513) 841 4545

Keywords: explosion hazard, dust, carbon, nanoparticle, nanomaterials

Statistical Correlations of the Explosion Parameters

As discussed in our first paper [Turkevich et al. 2014], the explosion severity index, K(500), is

highly correlated with the maximum explosion overpressure, Pm(500) [Figure 5 of Turkevich et al.

2014]; this high degree of correlation is confirmed (R2 = 0.9) between the global explosion

severity index, KSt, and the global maximum explosion pressure, Pmax

6 6.2 6.4 6.6 6.8 7 7.2 7.4 7.6 7.8 850

100

150

200

R² = 0.892895616252253

Pmax [bar]

KSt

[bar

-m/s

]

The minimum explosive concentration, MEC, is also highly correlated with both Pmax (R2 = 0.7)

and with KSt (R2 = 0.8)

6 6.2 6.4 6.6 6.8 7 7.2 7.4 7.6 7.8 80

10

20

30

40

50

60

70

80

90

100

R² = 0.744399300809449

Pmax [bar]

MEC

[g/

m3]

50 100 150 2000

10

20

30

40

50

60

70

80

90

100

R² = 0.795127085541348

KSt [bar-m/s]

MEC

[g/

m3]

As expected, the more explosive powders (high Pmax, high KSt) exhibit a lower concentration

threshold (MEC) for explosion.

However, the minimum ignition energy, MIE, is poorly correlated with both Pmax (R2 = 0.2) and

with KSt (R2 = 0.3)

6 6.2 6.4 6.6 6.8 7 7.2 7.4 7.6 7.8 80

0.5

1

1.5

2

R² = 0.243924285381389

Pmax [bar]

MIE

[kJ]

50 100 150 2000

0.5

1

1.5

2

R² = 0.295794243863882

KSt [bar-m/s]

MIE

[kJ]

Although the correlation is poor, the trend is as expected, namely the more explosive materials

(high Pmax, high KSt) exhibit a lower ignition threshold (MIE) for explosion. It is not surprising that

there is a similar lack of correlation (R2 = 0.2) between MIE and MEC

10 20 30 40 50 60 70 80 90 1000

0.5

1

1.5

2

R² = 0.216823903755842

MEC [g/m3]

MIE

[kJ

]

Again, while the correlation is poor, the trend is as expected, namely, the materials with a

low concentration threshold (MEC) also exhibit a low ignition threshold (MIE).

Similar behavior obtains for the minimum ignition cloud temperature: MITcloud is

reasonably correlated with both Pmax (R2 ~ 0.6) and KSt (R2 ~ 0.7)

6 6.5 7 7.5 8525

550

575

600

625

650

675R² = 0.640303102060147

Pmax [bar]

MITcl

oud [

oC]

50 100 150 200525

550

575

600

625

650

675

R² = 0.704284272858267

KSt [bar-m/s]MI

Tclou

d [oC

]

with the more explosive powders (high Pmax, high KSt) exhibiting a lower temperature

threshold (MITcloud) for explosion. There is poor correlation (R2 ~ 0.3) between MITcloud

and MEC and also (R2 ~ 0.3) between MITcloud and MIE

10 20 30 40 50 60 70 80 90 100525

550

575

600

625

650

675

R² = 0.30350964072569

MEC [g/m3]

MITcl

oud [

oC]

0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2525

550

575

600

625

650

675

R² = 0.267334271226269

MIE [kJ]

MITcl

oud [

oC]

Again, while the correlation is poor, in both cases, the trend is as expected, namely, that

materials with low concentration (MEC) and ignition (MIE) thresholds for explosion also

exhibit a low temperature threshold (MITcloud) for explosion.

Statistical Correlation with Aggregate Particle Size.

We believe that aggregation of the primary particles is not a significant determinant of the

explosion parameters. As indicated in the main paper, there is no evidence of any tightly bound

aggregates from our electron micrographs (either before or after explosion). We believe that

aggregation has, at best, a minimal effect on the explosion parameters of the carbonaceous

nanomaterials.

As discussed in the main paper, we have measured aggregate particle size distributions with

light scattering (CILAS 1064). We have attempted to correlate the various parameters that

characterize those distributions with the measured explosion parameters. The aggregate size

distributions are all broad and multimodal (main paper, Figure 1). Statistically, we may identify

a mean size, dmean, and the size of the mode (cumulant midpoint), d50; qualitatively, we may also

identify the size, ddom, of the dominant mode, as well as the sizes, dmax and dmin, of the largest and

smallest modes, respectively. As most of the weight is at the upper end of the distributions,

the parameters, dmean, d50, ddom, dmax are essentially equivalent.

There are weak statistical correlations (R2 ~ 0.6) of Pmax with dmean, d50, ddom, dmax

0 10 20 30 40 50 60 70 80 90 1006

6.5

7

7.5

8

R² = 0.619846400266592

d50 [micron]

Pmax

[ba

r]

0 20 40 60 80 1006

6.5

7

7.5

8

R² = 0.625585067270943

dmean [micron]

pmax

[bar]

0 20 40 60 80 100 1206

6.5

7

7.5

8

R² = 0.570021942174034

ddom [microns]

pmax

[bar]

0 20 40 60 80 100 1206

6.5

7

7.5

8

R² = 0.628707439388697

dmax [micron]

pmax

[bar]

There are similar weak statistical correlations (R2 ~ 0.6) of KSt with dmean, d50, ddom, dmax

0 20 40 60 80 10050

100

150

200

R² = 0.63476243026339

dmean [micron]

KSt [

bar-m

/s]

0 20 40 60 80 1000

50

100

150

200

250

R² = 0.645382997206696

d50 [micron]

KSt

[bar-m

/s]

0 20 40 60 80 100 12050

100

150

200

R² = 0.579519871402134

ddom [microns]

KSt [

bar-m

/s]

0 20 40 60 80 100 12050

100

150

200

R² = 0.603660166557892

dmax [micron]

KSt [

bar-m

/sec]

Statistically, the smaller the aggregate, the less explosive is the material—i.e. smaller Pmax and

smaller KSt. However, under the NanoSafe hypothesis, the smaller aggregates should be more

explosive. Thus the NanoSafe model is not supported by the statistical correlation.

With such a limited data set, it is impossible to deconvolute the effect of aggregate particle size

from the effect of allotrope on explosion severity; e.g. on the above correlation plots, the most

explosive material, fullerene (Pmax = 8 bar, KSt = 199 bar-m/s), is always upper right, and the least

explosive material, graphite (Pmax = 6.3 bar, KSt = 64 bar-m/s), is always lower left. Given the

established dependence of explosion severity on allotrope [Turkevich et al. 2014], it is difficult to

extract any additional influence of aggregate particle size on the severity of the carbonaceous

explosions.

For completeness, we have also examined the potential correlation with the lower end of the

distribution, dmin; there is poor correlation of both Pmax (R2 ~ 0.1) and KSt (R2 ~ 0.2) with dmin

.

0 2 4 6 8 10 12 14 16 18 206

6.5

7

7.5

8

R² = 0.0551443901744411

dmin [micron]

pmax

[bar]

0 5 10 15 2050

100

150

200

R² = 0.231259065983268

dmin [micron]

KSt [

bar-m

/sec]

Similarly, we have attempted to correlate MEC with aggregate particle size. The correlation is weak (R2 ~ 0.6) for

dmean, d50, ddom, dmax

0 20 40 60 80 1000

10

20

30

40

50

60

70

80

90

100

R² = 0.605699535555657

dmean [micron]

MEC [

g/m3

]

0 10 20 30 40 50 60 70 80 90 1000

10

20

30

40

50

60

70

80

90

100

R² = 0.622554170370054

d50 [micron]

MEC [

g/m3

]

0 20 40 60 80 100 1200

10

20

30

40

50

60

70

80

90

100

R² = 0.515696295380343

ddom [microns]

MEC [

g/m3

]

0 20 40 60 80 100 1200

10

20

30

40

50

60

70

80

90

100

R² = 0.565799154980731

dmax [micron]

MEC [

g/m3

]

Again, the weak statistical correlation contradicts the NanoSafe hypothesis, namely, while the

smaller aggregates should be more explosive, statistically, the smaller aggregates exhibit a

higher threshold MEC for explosion.

There is no correlation of MEC with dmin (R2 ~ 0.1)

0 5 10 15 200

10

20

30

40

50

60

70

80

90

100

R² = 0.0630170208584863

dmin [micron]

MEC

[g/m

3]

We have not attempted to correlate the more limited data sets for MIE, MITcloud with the

aggregate particle size distribution parameters.