As unlikely as it may seem, wood pellets can be dangerous. The risks associated with them are well documented and worth investigating if you are thinking of getting a biomass boiler that runs on pellets.
The most immediate danger comes from the risk of a dust explosion during delivery of the pellets. The risk should be minimised by electrical earth bonding all metal parts of the delivery system. You will notice the delivery driver will take care to earth his lorry before he starts the transfer of pellets. There should be no sources of ignition present during pellet delivery.
The second danger from the dust is respiratory in nature — this dust can suffocate you if you get enough of it into your lungs. Long term light to moderate exposure can also lead to respiratory problems, so always wear a good quality dust mask when handling pellets or whenever you are exposed to the dust.
Probably the most deadly risk comes from the carbon monoxide given off by the pellets. New pellets give off more than old ones, and wet pellets give off far more than dry ones. You should never enter a pellet store without fully appreciating all the risks and taking steps to assure your safety. The store should be well ventilated. Never enter before testing the air quality. Wear a harness and safety rope, and have somebody watching you at all times who is capable of dragging you out by the rope should you fall unconscious.
The following is taken from the HSE website:
Since 2010 there have been three deaths caused by entry into wood pellet storage facilities in domestic sites. Two were associated with a work activity and the other was a householder. In each case, the entry had been to resolve a technical problem.
In January 2010, a 43-year-old engineer died in Germany after he opened a pellet bunker door. A second worker who was standing right behind him was also affected but still able to call the emergency services. The pellet bunker had a storage capacity of approximately 155 tonnes of pellets, supplying about 700 households.
In November 2010 a 38-year-old male householder in Ireland died after entering the 7 tonne wood pellet storage room for his boiler. His wife and another man were treated in hospital after trying to pull him to safety.
In February 2011, the 28-year-old pregnant wife of a caretaker, acting on his behalf, died in Switzerland after entering an 82m3 pellet storeroom that supplied 60 households.
Note the one in Ireland was a small store serving only one household. The risk is very real.