Why wont the char set on fire?

Okay, so I made a fireball script that essentially burns any player it touches, however when the fireball makes contact with the player, an error shows up in huge quantities, and the player doesn't burn.

Note: The test subject for the fireball is a dummy

Error:12:24:31.510 - Workspace.Dummy.Regenerating Pad.Fire.Spread:7: attempt to perform arithmetic on field 'Size' (a userdata value) 12:24:31.510 - Stack Begin 12:24:31.511 - Script 'Workspace.Dummy.Regenerating Pad.Fire.Spread', Line 7 12:24:31.512 - Stack End

Script:

game.ReplicatedStorage.Fireball.OnServerEvent:connect(function(player, mousehit)
local char = game.Players[player.Name].Character
 local hum = char.Humanoid 
 local root = char.HumanoidRootPart




 local fireball = Instance.new("Part",workspace)
 local fire = game:GetService("ServerStorage").Fire
 fireball.Anchored = false
 fireball.CFrame = root.CFrame * CFrame.new(0,1,-4)
 fireball.Size = Vector3.new(2,2,2)
 fireball.Material = Enum.Material.Neon
 fireball.BrickColor = BrickColor.new("Deep orange")
 fireball.Shape = Enum.PartType.Ball
 fire:Clone().Parent = fireball




local bv = Instance.new("BodyVelocity")
 bv.MaxForce = Vector3.new(1e8,1e8,1e8)
 bv.Velocity = Vector3.new(0,0,0)
 bv.Parent = fireball
 ten = true
 local tween = game:GetService("TweenService")
 local tweeninfo = TweenInfo.new(1,Enum.EasingStyle.Linear,Enum.EasingDirection.Out,10,true,0)
 local tweenproperty = {Size = Vector3.new(5,5,5)}
 local tweenrun = tween:Create(fireball,tweeninfo,tweenproperty)
 tweenrun:Play()
 bv.Velocity = mousehit.lookVector*50
 game.Debris:AddItem(fireball, 10)

fireball.Touched:connect(function(hit)
 if not ten then return end
 ten = false
 local ehum = hit.Parent:findFirstChild("Humanoid") or hit.Parent.Parent:findFirstChild("Humanoid")
 if ehum and ehum ~= hum then
  fireball.CanCollide = false
  ehum:TakeDamage(10)
local debrisService = game:GetService("Debris")
local fire = game:GetService("ServerStorage"):FindFirstChild("Fire")
    for _, v in pairs(hit.Parent:GetChildren()) do
        if v:IsA("BasePart") then 
            if not v:FindFirstChild("Fire") then
                local fireClone = fire:Clone()
                fireClone.Parent = v
                debrisService:AddItem(fireClone, 5) -- removes the object in 5 seconds

end
end 
end
for i = 1, 10 do 
    hit.Parent.Humanoid:TakeDamage(1)
    wait(0.5)
end
  elseif hit.Parent == char then
  return nil
  elseif hit.Anchored  == true and hit.CanCollide == true then
  for i=1,50 do
   local part = fireball:clone()
   part.Size = Vector3.new(0.5,0.5,0.5)
   part.CFrame = fireball.CFrame
   part.CanCollide = false
   --part.BodyVelcoity.MaxForce = Vector3.new(1e8,0,1e8)
   part.Fire.LockedToPart = false
   part.BodyVelocity.Velocity = Vector3.new(math.random(-30,30),math.random(-30,30),math.random(-30,30))
   part.Parent = game.Workspace
   game.Debris:AddItem(part,1)

end 
fireball:Destroy()
ten = true
end
end)
end)

Fire spread script --Made by roblox

function Spread(part)
    check = part:findFirstChild("Fire")
        if check == nil then 
    script.Parent:Clone().Parent = part

        elseif check ~= nil then
    check.Size = check.Size + 1000000
    check.Heat = check.Heat  +1000000
    end
end


script.Parent.Parent.Touched:connect(Spread)