Dangerous (toxic) atmospheres in UK wood pellet and wood chip fuel storage

Figures & data

Table 1. Summary of site visit measurements.

Site	Sampling dates	CO (ppm)	CO2 (%)	O2 (%)	CH4 (%)	VOC (ppm)	Temperature (°C)	Ventilation rate (air changes per hour)	Microbiological Analysis
Site 2 Purpose built pellet store room.	28/2/13 for 19 days (24 days after last delivery.)	1 (0–2)	0.0	20.6 (20.5–21.4)	0.0	<1 (0–1)	18.1 (15.8–20.6)	1.7 (1.5–2.1)	All tests: not detected
Site 3 Converted barn wood chip store room.	20/2/13 for 28 days (1 day after last delivery & further weekly deliveries made)	1 (0–3)	0.1 (0.0–0.1)	19.5^a (15.4–21.0)	0.0	2 (0–29)	5.6 (0.0–10.2)	20.2 (12.8–25.9)	Bacteria (25°C): 1.81 × 10^7 cfu/g Bacteria (37°C): 2.61 × 10^6 cfu/g Mesophilic Fungi (25°C): 3.30 × 10^4 cfu/g
Site 4 Fabric pellet silo inside a former coal store room.	5/3/13 for 27 days (6 days after last delivery, 2nd delivery 8/4/13)	<1 (0–1)	<0.1 (0.0–0.1)	19.1^a (16.0–26.8)	0.0	<1 (0–1)	8.2 (5.6–10.8)	8.8 (8.6–9.1)	All test: not detected
Site 6 Fabric pellet silo in a boiler room.	11/3/13 for 31 days (33 days after last delivery. 2nd delivery 21/3/13)	<1 (0–3)	<0.1 (0.0–0.1)	20.9 (20.0–21.0)	0.0	<1 (0–1)	23.9 (10.3–26.9)	2.8 (2.0–3.5)	No sample collected, pellets inaccessible
Site 7 Large-scale pellet storage in a former grain warehouse.	11/9/13 for 29 days (∼68 days after delivery >120 days after production).	5 (0–27)	<0.1 (0.0–0.1)	20.2 (19.5–20.8)	0.0	1 (0–11)	12.9 (5.8–22.1)	Estimated 0.5–2	Mesophilic Fungi: (25°C): 125 cfu/g Aspergillus fumigatus: (40°C): low levels

CO – carbon monoxide; CO₂ – carbon dioxide; O₂ – oxygen; CH₄ – methane; VOC – volatile organic compounds

 Site 1 (outdoor GRP tower silo) and Site 5 (converted coal store room) not included in testing because of access problems.

Air measurements are means (ranges in brackets)

cfu/g – colony forming units per gram

^athe reliability of these data is discussed in the text.

Table 2. Emission concentrations produced in laboratory headspace air composition tests and estimated indicative emission factors.

			Carbon monoxide		Carbon dioxide
			Maximum	Emission		Emission	Oxygen	VOCs
Test	Mass (kg)	Period (days)	(ppm)	(mg/kg)	Maximum (%)	(mg/kg)	Minimum (%)	Maximum (ppm)
Wood pellets^c	28.2	34	>1042^a	>1.6	15.47^b	21.8	0.1	47
Undried wood chips^d	3.6	15	60^b	1.1	35.57	650	5.7	2481
Dried wood chips^d	3.0	11	543^b	11.4	0.15^b	31.5	20.9	73

^ainstrument off scale.

^breading still increasing.

^cunseasoned virgin pine wood dust.

^dalmost entirely seasoned spruce.

Figure 1. Site 7 carbon monoxide concentrations.

Figure 2. Laboratory monitoring of air composition above wood pellets (flammable concentration not shown because it did not rise above zero).

Figure 3. Laboratory monitoring of air composition above undried wood chips (flammable concentration not shown because it did not rise above zero).

Figure 4. Laboratory monitoring of air composition above dried wood chips (flammable concentration not shown because it did not rise above zero).