In using tear gas, one inherent risk mentioned earlier by Coronach is the possibility of fire. Factors contributing to the fire are highly inflammable objects which the occupant has laying around. Why then does LE still use tear gas?
Because it remains the lesser of two evils. Certainly you can besiege the house, but then you risk innocent parties being hurt. Evacuation is required for a reasonable distance (depends on density of housing, type of materials used in constructing the house, walls (brick, concrete, wood) which surround the garden, personnel available. So you can storm a house, but remember that one deputy/officer is already dead. Do you want to risk losing more officers? No. Storming then may be unfeasible and awaiting to talk the guy out may well be too. Hence, LE resorts to the immediate method at hand: tear gas. The vast majority of times tear gas will work without causing permanent damage. Furthermore, most modern tear gas bombs are non-incendiary in nature. You can thank the SLA for that.
Vigilantibus et non dormientibus jura subveniunt. Molon Labe!